core
¶
Core objects
|
Run tests for module using nose. |
Module: core.geometry
¶
Utility functions for algebra etc
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Return angles for Cartesian 3D coordinates x, y, and z |
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Cartesian distance between pts1 and pts2 |
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a, b and c are 3-dimensional vectors which are the vertices of a triangle. |
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Return 4x4 transformation matrix from sequence of transformations. |
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Compose multiple 4x4 affine transformations in one 4x4 matrix |
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Return sequence of transformations from transformation matrix. |
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Calculate the maximal distance from the center to a corner of a voxel, given an affine |
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Return homogeneous rotation matrix from Euler angles and axis sequence. |
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Test whether all points on a unit sphere lie in the same hemisphere. |
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Lambert Equal Area Projection from cartesian vector to plane |
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Lambert Equal Area Projection from polar sphere to plane |
Least squares positive semi-definite tensor estimation |
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Return vector divided by its Euclidean (L2) norm |
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Computes n evenly spaced perpendicular directions relative to a given vector v |
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Rodrigues formula |
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Convert spherical coordinates to latitude and longitude. |
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Spherical to Cartesian coordinates |
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Distance across sphere surface between pts1 and pts2 |
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rotation matrix from 2 unit vectors |
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Cosine of angle between two (sets of) vectors |
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Return vector Euclidean (L2) norm |
Module: core.gradients
¶
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Diffusion gradient information |
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Points on the unit sphere. |
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Decorator to create OneTimeProperty attributes. |
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Check if you have enough different b-values in your gradient table |
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Models electrostatic repulsion on the unit sphere |
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Generates N bvectors. |
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A general function for creating diffusion MR gradients. |
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Creates a GradientTable from a bvals array and a bvecs array |
A general function for creating diffusion MR gradients. |
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A general function for creating diffusion MR gradients. |
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Compute the inverse of a matrix. |
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Compute the polar decomposition. |
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Reorient the directions in a GradientTable. |
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“This function rounds the b-values |
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This function gives the unique rounded b-values of the data |
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Return vector Euclidean (L2) norm |
Issue a warning, or maybe ignore it or raise an exception. |
Module: core.ndindex
¶
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Create a view into the array with the given shape and strides. |
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An N-dimensional iterator object to index arrays. |
Module: core.onetime
¶
Descriptor support for NIPY.
Copyright (c) 2006-2011, NIPY Developers All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
- Neither the name of the NIPY Developers nor the names of any
contributors may be used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Utilities to support special Python descriptors [1,2], in particular the use of a useful pattern for properties we call ‘one time properties’. These are object attributes which are declared as properties, but become regular attributes once they’ve been read the first time. They can thus be evaluated later in the object’s life cycle, but once evaluated they become normal, static attributes with no function call overhead on access or any other constraints.
A special ResetMixin class is provided to add a .reset() method to users who may want to have their objects capable of resetting these computed properties to their ‘untriggered’ state.
References¶
[1] How-To Guide for Descriptors, Raymond Hettinger. http://users.rcn.com/python/download/Descriptor.htm
[2] Python data model, http://docs.python.org/reference/datamodel.html
|
A descriptor to make special properties that become normal attributes. |
A Mixin class to add a .reset() method to users of OneTimeProperty. |
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|
Decorator to create OneTimeProperty attributes. |
Module: core.optimize
¶
A unified interface for performing and debugging optimization problems.
|
A sklearn-like interface to scipy.optimize.nnls |
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|
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Provide a sklearn-like uniform interface to algorithms that solve problems of the form: \(y = Ax\) for \(x\) |
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Minimization of scalar function of one or more variables. |
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Solve y=Xh for h, using gradient descent, with X a sparse matrix. |
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The same as np.dot(A, B), except it works even if A or B or both are sparse matrices. |
Module: core.profile
¶
Class for profiling cython code
|
Profile python/cython files or functions |
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Return package-like thing and module setup for package name |
Module: core.rng
¶
Random number generation utilities
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Generate uniformly distributed random numbers using the 32-bit generator from figure 3 of: L’Ecuyer, P. |
Algorithm AS 183 Appl. |
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B.A. |
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Queries the given executable (defaults to the Python interpreter binary) for various architecture information. |
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Return the floor of x as an Integral. |
Module: core.sphere
¶
|
Points on the unit sphere. |
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Points on the unit sphere. |
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Decorator to create OneTimeProperty attributes. |
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Return angles for Cartesian 3D coordinates x, y, and z |
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Models electrostatic repulsion on the unit sphere |
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Checks the euler characteristic of a sphere |
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Triangulate a set of vertices on the sphere. |
Remove vertices that are less than theta degrees from any other |
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Spherical to Cartesian coordinates |
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Extract all unique edges from given triangular faces. |
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Remove duplicate sets. |
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Return vector Euclidean (L2) norm |
Module: core.sphere_stats
¶
Statistics on spheres
permutations(iterable[, r]) –> permutations object |
|
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Computes the cosine distance of the best match between points of two sets of vectors S and T |
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Computes the mean cosine distance of the best match between points of two sets of vectors S and T (angular similarity) |
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Principal direction and confidence ellipse |
|
Random unit vectors from a uniform distribution on the sphere. |
Module: core.subdivide_octahedron
¶
Create a unit sphere by subdividing all triangles of an octahedron recursively.
The unit sphere has a radius of 1, which also means that all points in this sphere (assumed to have centre at [0, 0, 0]) have an absolute value (modulus) of 1. Another feature of the unit sphere is that the unit normals of this sphere are exactly the same as the vertices.
This recursive method will avoid the common problem of the polar singularity, produced by 2d (lon-lat) parameterization methods.
|
Points on the unit sphere. |
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Creates a unit sphere by subdividing a unit octahedron, returns half the sphere. |
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Creates a unit sphere by subdividing a unit octahedron. |
Module: core.wavelet
¶
|
3D Analysis Filter Bank |
|
3D Analysis Filter Bank |
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3D Circular Shift |
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3-D Discrete Wavelet Transform |
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Inverse 3-D Discrete Wavelet Transform |
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Function generating inverse of the permutation |
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3D Synthesis Filter Bank |
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3D Synthesis Filter Bank |
test¶
-
dipy.core.
test
(label='fast', verbose=1, extra_argv=None, doctests=False, coverage=False, raise_warnings=None, timer=False)¶ Run tests for module using nose.
- Parameters
- label{‘fast’, ‘full’, ‘’, attribute identifier}, optional
Identifies the tests to run. This can be a string to pass to the nosetests executable with the ‘-A’ option, or one of several special values. Special values are:
‘fast’ - the default - which corresponds to the
nosetests -A
option of ‘not slow’.‘full’ - fast (as above) and slow tests as in the ‘no -A’ option to nosetests - this is the same as ‘’.
None or ‘’ - run all tests.
attribute_identifier - string passed directly to nosetests as ‘-A’.
- verboseint, optional
Verbosity value for test outputs, in the range 1-10. Default is 1.
- extra_argvlist, optional
List with any extra arguments to pass to nosetests.
- doctestsbool, optional
If True, run doctests in module. Default is False.
- coveragebool, optional
If True, report coverage of NumPy code. Default is False. (This requires the coverage module).
- raise_warningsNone, str or sequence of warnings, optional
This specifies which warnings to configure as ‘raise’ instead of being shown once during the test execution. Valid strings are:
“develop” : equals
(Warning,)
“release” : equals
()
, do not raise on any warnings.
- timerbool or int, optional
Timing of individual tests with
nose-timer
(which needs to be installed). If True, time tests and report on all of them. If an integer (sayN
), report timing results forN
slowest tests.
- Returns
- resultobject
Returns the result of running the tests as a
nose.result.TextTestResult
object.
Notes
Each NumPy module exposes test in its namespace to run all tests for it. For example, to run all tests for numpy.lib:
>>> np.lib.test() #doctest: +SKIP
Examples
>>> result = np.lib.test() #doctest: +SKIP Running unit tests for numpy.lib ... Ran 976 tests in 3.933s
OK
>>> result.errors #doctest: +SKIP [] >>> result.knownfail #doctest: +SKIP []
cart2sphere¶
-
dipy.core.geometry.
cart2sphere
(x, y, z)¶ Return angles for Cartesian 3D coordinates x, y, and z
See doc for
sphere2cart
for angle conventions and derivation of the formulae.\(0\le\theta\mathrm{(theta)}\le\pi\) and \(-\pi\le\phi\mathrm{(phi)}\le\pi\)
- Parameters
- xarray_like
x coordinate in Cartesian space
- yarray_like
y coordinate in Cartesian space
- zarray_like
z coordinate
- Returns
- rarray
radius
- thetaarray
inclination (polar) angle
- phiarray
azimuth angle
cart_distance¶
-
dipy.core.geometry.
cart_distance
(pts1, pts2)¶ Cartesian distance between pts1 and pts2
If either of pts1 or pts2 is 2D, then we take the first dimension to index points, and the second indexes coordinate. More generally, we take the last dimension to be the coordinate dimension.
- Parameters
- pts1(N,R) or (R,) array_like
where N is the number of points and R is the number of coordinates defining a point (
R==3
for 3D)- pts2(N,R) or (R,) array_like
where N is the number of points and R is the number of coordinates defining a point (
R==3
for 3D). It should be possible to broadcast pts1 against pts2
- Returns
- d(N,) or (0,) array
Cartesian distances between corresponding points in pts1 and pts2
See also
sphere_distance
distance between points on sphere surface
Examples
>>> cart_distance([0,0,0], [0,0,3]) 3.0
circumradius¶
-
dipy.core.geometry.
circumradius
(a, b, c)¶ a, b and c are 3-dimensional vectors which are the vertices of a triangle. The function returns the circumradius of the triangle, i.e the radius of the smallest circle that can contain the triangle. In the degenerate case when the 3 points are collinear it returns half the distance between the furthest apart points.
- Parameters
- a, b, c(3,) array_like
the three vertices of the triangle
- Returns
- circumradiusfloat
the desired circumradius
compose_matrix¶
-
dipy.core.geometry.
compose_matrix
(scale=None, shear=None, angles=None, translate=None, perspective=None)¶ Return 4x4 transformation matrix from sequence of transformations.
Code modified from the work of Christoph Gohlke link provided here http://www.lfd.uci.edu/~gohlke/code/transformations.py.html
This is the inverse of the
decompose_matrix
function.- Parameters
- scale(3,) array_like
Scaling factors.
- sheararray_like
Shear factors for x-y, x-z, y-z axes.
- anglesarray_like
Euler angles about static x, y, z axes.
- translatearray_like
Translation vector along x, y, z axes.
- perspectivearray_like
Perspective partition of matrix.
- Returns
- matrix4x4 array
Examples
>>> import math >>> import numpy as np >>> import dipy.core.geometry as gm >>> scale = np.random.random(3) - 0.5 >>> shear = np.random.random(3) - 0.5 >>> angles = (np.random.random(3) - 0.5) * (2*math.pi) >>> trans = np.random.random(3) - 0.5 >>> persp = np.random.random(4) - 0.5 >>> M0 = gm.compose_matrix(scale, shear, angles, trans, persp)
compose_transformations¶
-
dipy.core.geometry.
compose_transformations
(*mats)¶ Compose multiple 4x4 affine transformations in one 4x4 matrix
- Parameters
- mat1array, (4, 4)
- mat2array, (4, 4)
- …
- matNarray, (4, 4)
- Returns
- matN x … x mat2 x mat1array, (4, 4)
decompose_matrix¶
-
dipy.core.geometry.
decompose_matrix
(matrix)¶ Return sequence of transformations from transformation matrix.
Code modified from the excellent work of Christoph Gohlke link provided here: http://www.lfd.uci.edu/~gohlke/code/transformations.py.html
- Parameters
- matrixarray_like
Non-degenerative homogeneous transformation matrix
- Returns
- scale(3,) ndarray
Three scaling factors.
- shear(3,) ndarray
Shear factors for x-y, x-z, y-z axes.
- angles(3,) ndarray
Euler angles about static x, y, z axes.
- translate(3,) ndarray
Translation vector along x, y, z axes.
- perspectivendarray
Perspective partition of matrix.
- Raises
- ValueError
If matrix is of wrong type or degenerative.
Examples
>>> import numpy as np >>> T0=np.diag([2,1,1,1]) >>> scale, shear, angles, trans, persp = decompose_matrix(T0)
dist_to_corner¶
-
dipy.core.geometry.
dist_to_corner
(affine)¶ Calculate the maximal distance from the center to a corner of a voxel, given an affine
- Parameters
- affine4 by 4 array.
The spatial transformation from the measurement to the scanner space.
- Returns
- dist: float
The maximal distance to the corner of a voxel, given voxel size encoded in the affine.
euler_matrix¶
-
dipy.core.geometry.
euler_matrix
(ai, aj, ak, axes='sxyz')¶ Return homogeneous rotation matrix from Euler angles and axis sequence.
Code modified from the work of Christoph Gohlke link provided here http://www.lfd.uci.edu/~gohlke/code/transformations.py.html
- Parameters
- ai, aj, akEuler’s roll, pitch and yaw angles
- axesOne of 24 axis sequences as string or encoded tuple
- Returns
- matrixndarray (4, 4)
- Code modified from the work of Christoph Gohlke link provided here
- http://www.lfd.uci.edu/~gohlke/code/transformations.py.html
Examples
>>> import numpy >>> R = euler_matrix(1, 2, 3, 'syxz') >>> numpy.allclose(numpy.sum(R[0]), -1.34786452) True >>> R = euler_matrix(1, 2, 3, (0, 1, 0, 1)) >>> numpy.allclose(numpy.sum(R[0]), -0.383436184) True >>> ai, aj, ak = (4.0*math.pi) * (numpy.random.random(3) - 0.5) >>> for axes in _AXES2TUPLE.keys(): ... _ = euler_matrix(ai, aj, ak, axes) >>> for axes in _TUPLE2AXES.keys(): ... _ = euler_matrix(ai, aj, ak, axes)
is_hemispherical¶
-
dipy.core.geometry.
is_hemispherical
(vecs)¶ Test whether all points on a unit sphere lie in the same hemisphere.
- Parameters
- vecsnumpy.ndarray
2D numpy array with shape (N, 3) where N is the number of points. All points must lie on the unit sphere.
- Returns
- is_hemibool
If True, one can find a hemisphere that contains all the points. If False, then the points do not lie in any hemisphere
- polenumpy.ndarray
If is_hemi == True, then pole is the “central” pole of the input vectors. Otherwise, pole is the zero vector.
References
https://rstudio-pubs-static.s3.amazonaws.com/27121_a22e51b47c544980bad594d5e0bb2d04.html # noqa
lambert_equal_area_projection_cart¶
-
dipy.core.geometry.
lambert_equal_area_projection_cart
(x, y, z)¶ Lambert Equal Area Projection from cartesian vector to plane
Return positions in \((y_1,y_2)\) plane corresponding to the directions of the vectors with cartesian coordinates xyz under the Lambert Equal Area Projection mapping (see Mardia and Jupp (2000), Directional Statistics, p. 161).
The Lambert EAP maps the upper hemisphere to the planar disc of radius 1 and the lower hemisphere to the planar annulus between radii 1 and 2, The Lambert EAP maps the upper hemisphere to the planar disc of radius 1 and the lower hemisphere to the planar annulus between radii 1 and 2. and vice versa.
See doc for
sphere2cart
for angle conventions- Parameters
- xarray_like
x coordinate in Cartesion space
- yarray_like
y coordinate in Cartesian space
- zarray_like
z coordinate
- Returns
- y(N,2) array
planar coordinates of points following mapping by Lambert’s EAP.
lambert_equal_area_projection_polar¶
-
dipy.core.geometry.
lambert_equal_area_projection_polar
(theta, phi)¶ Lambert Equal Area Projection from polar sphere to plane
Return positions in (y1,y2) plane corresponding to the points with polar coordinates (theta, phi) on the unit sphere, under the Lambert Equal Area Projection mapping (see Mardia and Jupp (2000), Directional Statistics, p. 161).
See doc for
sphere2cart
for angle conventions\(0 \le \theta \le \pi\) and \(0 \le \phi \le 2 \pi\)
\(|(y_1,y_2)| \le 2\)
The Lambert EAP maps the upper hemisphere to the planar disc of radius 1 and the lower hemisphere to the planar annulus between radii 1 and 2, and vice versa.
- Parameters
- thetaarray_like
theta spherical coordinates
- phiarray_like
phi spherical coordinates
- Returns
- y(N,2) array
planar coordinates of points following mapping by Lambert’s EAP.
nearest_pos_semi_def¶
-
dipy.core.geometry.
nearest_pos_semi_def
(B)¶ Least squares positive semi-definite tensor estimation
- Parameters
- B(3,3) array_like
B matrix - symmetric. We do not check the symmetry.
- Returns
- npds(3,3) array
Estimated nearest positive semi-definite array to matrix B.
References
- 1
Niethammer M, San Jose Estepar R, Bouix S, Shenton M, Westin CF. On diffusion tensor estimation. Conf Proc IEEE Eng Med Biol Soc. 2006;1:2622-5. PubMed PMID: 17946125; PubMed Central PMCID: PMC2791793.
Examples
>>> B = np.diag([1, 1, -1]) >>> nearest_pos_semi_def(B) array([[ 0.75, 0. , 0. ], [ 0. , 0.75, 0. ], [ 0. , 0. , 0. ]])
normalized_vector¶
-
dipy.core.geometry.
normalized_vector
(vec, axis=-1)¶ Return vector divided by its Euclidean (L2) norm
See unit vector and Euclidean norm
- Parameters
- vecarray_like shape (3,)
- Returns
- nvecarray shape (3,)
vector divided by L2 norm
Examples
>>> vec = [1, 2, 3] >>> l2n = np.sqrt(np.dot(vec, vec)) >>> nvec = normalized_vector(vec) >>> np.allclose(np.array(vec) / l2n, nvec) True >>> vec = np.array([[1, 2, 3]]) >>> vec.shape == (1, 3) True >>> normalized_vector(vec).shape == (1, 3) True
perpendicular_directions¶
-
dipy.core.geometry.
perpendicular_directions
(v, num=30, half=False)¶ Computes n evenly spaced perpendicular directions relative to a given vector v
- Parameters
- varray (3,)
Array containing the three cartesian coordinates of vector v
- numint, optional
Number of perpendicular directions to generate
- halfbool, optional
If half is True, perpendicular directions are sampled on half of the unit circumference perpendicular to v, otherwive perpendicular directions are sampled on the full circumference. Default of half is False
- Returns
- psamplesarray (n, 3)
array of vectors perpendicular to v
Notes
Perpendicular directions are estimated using the following two step procedure:
1) the perpendicular directions are first sampled in a unit circumference parallel to the plane normal to the x-axis.
2) Samples are then rotated and aligned to the plane normal to vector v. The rotational matrix for this rotation is constructed as reference frame basis which axis are the following:
The first axis is vector v
The second axis is defined as the normalized vector given by the
cross product between vector v and the unit vector aligned to the x-axis - The third axis is defined as the cross product between the previous computed vector and vector v.
Following this two steps, coordinates of the final perpendicular directions are given as:
\[\left [ -\sin(a_{i}) \sqrt{{v_{y}}^{2}+{v_{z}}^{2}} \; , \; \frac{v_{x}v_{y}\sin(a_{i})-v_{z}\cos(a_{i})} {\sqrt{{v_{y}}^{2}+{v_{z}}^{2}}} \; , \; \frac{v_{x}v_{z}\sin(a_{i})-v_{y}\cos(a_{i})} {\sqrt{{v_{y}}^{2}+{v_{z}}^{2}}} \right ]\]This procedure has a singularity when vector v is aligned to the x-axis. To solve this singularity, perpendicular directions in procedure’s step 1 are defined in the plane normal to y-axis and the second axis of the rotated frame of reference is computed as the normalized vector given by the cross product between vector v and the unit vector aligned to the y-axis. Following this, the coordinates of the perpendicular directions are given as:
left [ -frac{left (v_{x}v_{y}sin(a_{i})+v_{z}cos(a_{i}) right )} {sqrt{{v_{x}}^{2}+{v_{z}}^{2}}} ; , ; sin(a_{i}) sqrt{{v_{x}}^{2}+{v_{z}}^{2}} ; , ; frac{v_{y}v_{z}sin(a_{i})+v_{x}cos(a_{i})} {sqrt{{v_{x}}^{2}+{v_{z}}^{2}}} right ]
For more details on this calculation, see ` here <http://gsoc2015dipydki.blogspot.it/2015/07/rnh-post-8-computing-perpendicular.html>`_.
rodrigues_axis_rotation¶
-
dipy.core.geometry.
rodrigues_axis_rotation
(r, theta)¶ Rodrigues formula
Rotation matrix for rotation around axis r for angle theta.
The rotation matrix is given by the Rodrigues formula:
R = Id + sin(theta)*Sn + (1-cos(theta))*Sn^2
with:
0 -nz ny Sn = nz 0 -nx -ny nx 0
where n = r / ||r||
In case the angle ||r|| is very small, the above formula may lead to numerical instabilities. We instead use a Taylor expansion around theta=0:
R = I + sin(theta)/tetha Sr + (1-cos(theta))/teta2 Sr^2
leading to:
R = I + (1-theta2/6)*Sr + (1/2-theta2/24)*Sr^2
- Parameters
- rarray_like shape (3,), axis
- thetafloat, angle in degrees
- Returns
- Rarray, shape (3,3), rotation matrix
Examples
>>> import numpy as np >>> from dipy.core.geometry import rodrigues_axis_rotation >>> v=np.array([0,0,1]) >>> u=np.array([1,0,0]) >>> R=rodrigues_axis_rotation(v,40) >>> ur=np.dot(R,u) >>> np.round(np.rad2deg(np.arccos(np.dot(ur,u)))) 40.0
sph2latlon¶
-
dipy.core.geometry.
sph2latlon
(theta, phi)¶ Convert spherical coordinates to latitude and longitude.
- Returns
- lat, lonndarray
Latitude and longitude.
sphere2cart¶
-
dipy.core.geometry.
sphere2cart
(r, theta, phi)¶ Spherical to Cartesian coordinates
This is the standard physics convention where theta is the inclination (polar) angle, and phi is the azimuth angle.
Imagine a sphere with center (0,0,0). Orient it with the z axis running south-north, the y axis running west-east and the x axis from posterior to anterior. theta (the inclination angle) is the angle to rotate from the z-axis (the zenith) around the y-axis, towards the x axis. Thus the rotation is counter-clockwise from the point of view of positive y. phi (azimuth) gives the angle of rotation around the z-axis towards the y axis. The rotation is counter-clockwise from the point of view of positive z.
Equivalently, given a point P on the sphere, with coordinates x, y, z, theta is the angle between P and the z-axis, and phi is the angle between the projection of P onto the XY plane, and the X axis.
Geographical nomenclature designates theta as ‘co-latitude’, and phi as ‘longitude’
- Parameters
- rarray_like
radius
- thetaarray_like
inclination or polar angle
- phiarray_like
azimuth angle
- Returns
- xarray
x coordinate(s) in Cartesion space
- yarray
y coordinate(s) in Cartesian space
- zarray
z coordinate
Notes
See these pages:
for excellent discussion of the many different conventions possible. Here we use the physics conventions, used in the wikipedia page.
Derivations of the formulae are simple. Consider a vector x, y, z of length r (norm of x, y, z). The inclination angle (theta) can be found from: cos(theta) == z / r -> z == r * cos(theta). This gives the hypotenuse of the projection onto the XY plane, which we will call Q. Q == r*sin(theta). Now x / Q == cos(phi) -> x == r * sin(theta) * cos(phi) and so on.
We have deliberately named this function
sphere2cart
rather thansph2cart
to distinguish it from the Matlab function of that name, because the Matlab function uses an unusual convention for the angles that we did not want to replicate. The Matlab function is trivial to implement with the formulae given in the Matlab help.
sphere_distance¶
-
dipy.core.geometry.
sphere_distance
(pts1, pts2, radius=None, check_radius=True)¶ Distance across sphere surface between pts1 and pts2
- Parameters
- pts1(N,R) or (R,) array_like
where N is the number of points and R is the number of coordinates defining a point (
R==3
for 3D)- pts2(N,R) or (R,) array_like
where N is the number of points and R is the number of coordinates defining a point (
R==3
for 3D). It should be possible to broadcast pts1 against pts2- radiusNone or float, optional
Radius of sphere. Default is to work out radius from mean of the length of each point vector
- check_radiusbool, optional
If True, check if the points are on the sphere surface - i.e check if the vector lengths in pts1 and pts2 are close to radius. Default is True.
- Returns
- d(N,) or (0,) array
Distances between corresponding points in pts1 and pts2 across the spherical surface, i.e. the great circle distance
See also
cart_distance
cartesian distance between points
vector_cosine
cosine of angle between vectors
Examples
>>> print('%.4f' % sphere_distance([0,1],[1,0])) 1.5708 >>> print('%.4f' % sphere_distance([0,3],[3,0])) 4.7124
vec2vec_rotmat¶
-
dipy.core.geometry.
vec2vec_rotmat
(u, v)¶ rotation matrix from 2 unit vectors
u, v being unit 3d vectors return a 3x3 rotation matrix R than aligns u to v.
In general there are many rotations that will map u to v. If S is any rotation using v as an axis then R.S will also map u to v since (S.R)u = S(Ru) = Sv = v. The rotation R returned by vec2vec_rotmat leaves fixed the perpendicular to the plane spanned by u and v.
The transpose of R will align v to u.
- Parameters
- uarray, shape(3,)
- varray, shape(3,)
- Returns
- Rarray, shape(3,3)
Examples
>>> import numpy as np >>> from dipy.core.geometry import vec2vec_rotmat >>> u=np.array([1,0,0]) >>> v=np.array([0,1,0]) >>> R=vec2vec_rotmat(u,v) >>> np.dot(R,u) array([ 0., 1., 0.]) >>> np.dot(R.T,v) array([ 1., 0., 0.])
vector_cosine¶
-
dipy.core.geometry.
vector_cosine
(vecs1, vecs2)¶ Cosine of angle between two (sets of) vectors
The cosine of the angle between two vectors
v1
andv2
is given by the inner product ofv1
andv2
divided by the product of the vector lengths:v_cos = np.inner(v1, v2) / (np.sqrt(np.sum(v1**2)) * np.sqrt(np.sum(v2**2)))
- Parameters
- vecs1(N, R) or (R,) array_like
N vectors (as rows) or single vector. Vectors have R elements.
- vecs1(N, R) or (R,) array_like
N vectors (as rows) or single vector. Vectors have R elements. It should be possible to broadcast vecs1 against vecs2
- Returns
- vcos(N,) or (0,) array
Vector cosines. To get the angles you will need
np.arccos
Notes
The vector cosine will be the same as the correlation only if all the input vectors have zero mean.
vector_norm¶
-
dipy.core.geometry.
vector_norm
(vec, axis=-1, keepdims=False)¶ Return vector Euclidean (L2) norm
See unit vector and Euclidean norm
- Parameters
- vecarray_like
Vectors to norm.
- axisint
Axis over which to norm. By default norm over last axis. If axis is None, vec is flattened then normed.
- keepdimsbool
If True, the output will have the same number of dimensions as vec, with shape 1 on axis.
- Returns
- normarray
Euclidean norms of vectors.
Examples
>>> import numpy as np >>> vec = [[8, 15, 0], [0, 36, 77]] >>> vector_norm(vec) array([ 17., 85.]) >>> vector_norm(vec, keepdims=True) array([[ 17.], [ 85.]]) >>> vector_norm(vec, axis=0) array([ 8., 39., 77.])
GradientTable
¶
-
class
dipy.core.gradients.
GradientTable
(gradients, big_delta=None, small_delta=None, b0_threshold=50)¶ Bases:
object
Diffusion gradient information
- Parameters
- gradientsarray_like (N, 3)
Diffusion gradients. The direction of each of these vectors corresponds to the b-vector, and the length corresponds to the b-value.
- b0_thresholdfloat
Gradients with b-value less than or equal to b0_threshold are considered as b0s i.e. without diffusion weighting.
See also
Notes
The GradientTable object is immutable. Do NOT assign attributes. If you have your gradient table in a bval & bvec format, we recommend using the factory function gradient_table
- Attributes
- gradients(N,3) ndarray
diffusion gradients
- bvals(N,) ndarray
The b-value, or magnitude, of each gradient direction.
- qvals: (N,) ndarray
The q-value for each gradient direction. Needs big and small delta.
- bvecs(N,3) ndarray
The direction, represented as a unit vector, of each gradient.
- b0s_mask(N,) ndarray
Boolean array indicating which gradients have no diffusion weighting, ie b-value is close to 0.
- b0_thresholdfloat
Gradients with b-value less than or equal to b0_threshold are considered to not have diffusion weighting.
Methods
b0s_mask
bvals
bvecs
gradient_strength
qvals
tau
-
__init__
(gradients, big_delta=None, small_delta=None, b0_threshold=50)¶ Constructor for GradientTable class
-
b0s_mask
()¶
-
bvals
()¶
-
bvecs
()¶
-
gradient_strength
()¶
-
property
info
¶
-
qvals
()¶
-
tau
()¶
HemiSphere
¶
-
class
dipy.core.gradients.
HemiSphere
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None, tol=1e-05)¶ Bases:
dipy.core.sphere.Sphere
Points on the unit sphere.
A HemiSphere is similar to a Sphere but it takes antipodal symmetry into account. Antipodal symmetry means that point v on a HemiSphere is the same as the point -v. Duplicate points are discarded when constructing a HemiSphere (including antipodal duplicates). edges and faces are remapped to the remaining points as closely as possible.
The HemiSphere can be constructed using one of three conventions:
HemiSphere(x, y, z) HemiSphere(xyz=xyz) HemiSphere(theta=theta, phi=phi)
- Parameters
- x, y, z1-D array_like
Vertices as x-y-z coordinates.
- theta, phi1-D array_like
Vertices as spherical coordinates. Theta and phi are the inclination and azimuth angles respectively.
- xyz(N, 3) ndarray
Vertices as x-y-z coordinates.
- faces(N, 3) ndarray
Indices into vertices that form triangular faces. If unspecified, the faces are computed using a Delaunay triangulation.
- edges(N, 2) ndarray
Edges between vertices. If unspecified, the edges are derived from the faces.
- tolfloat
Angle in degrees. Vertices that are less than tol degrees apart are treated as duplicates.
See also
Sphere
- Attributes
- x
- y
- z
Methods
find_closest
(xyz)Find the index of the vertex in the Sphere closest to the input vector, taking into account antipodal symmetry
from_sphere
(sphere[, tol])Create instance from a Sphere
mirror
()Create a full Sphere from a HemiSphere
subdivide
([n])Create a more subdivided HemiSphere
edges
faces
vertices
-
__init__
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None, tol=1e-05)¶ Create a HemiSphere from points
-
faces
()¶
-
find_closest
(xyz)¶ Find the index of the vertex in the Sphere closest to the input vector, taking into account antipodal symmetry
- Parameters
- xyzarray-like, 3 elements
A unit vector
- Returns
- idxint
The index into the Sphere.vertices array that gives the closest vertex (in angle).
-
classmethod
from_sphere
(sphere, tol=1e-05)¶ Create instance from a Sphere
-
mirror
()¶ Create a full Sphere from a HemiSphere
-
subdivide
(n=1)¶ Create a more subdivided HemiSphere
See Sphere.subdivide for full documentation.
auto_attr¶
-
dipy.core.gradients.
auto_attr
(func)¶ Decorator to create OneTimeProperty attributes.
- Parameters
- funcmethod
The method that will be called the first time to compute a value. Afterwards, the method’s name will be a standard attribute holding the value of this computation.
Examples
>>> class MagicProp(object): ... @auto_attr ... def a(self): ... return 99 ... >>> x = MagicProp() >>> 'a' in x.__dict__ False >>> x.a 99 >>> 'a' in x.__dict__ True
check_multi_b¶
-
dipy.core.gradients.
check_multi_b
(gtab, n_bvals, non_zero=True, bmag=None)¶ Check if you have enough different b-values in your gradient table
- Parameters
- gtabGradientTable class instance.
- n_bvalsint
The number of different b-values you are checking for.
- non_zerobool
Whether to check only non-zero bvalues. In this case, we will require at least n_bvals non-zero b-values (where non-zero is defined depending on the gtab object’s b0_threshold attribute)
- bmagint
The order of magnitude of the b-values used. The function will normalize the b-values relative \(10^{bmag}\). Default: derive this value from the maximal b-value provided: \(bmag=log_{10}(max(bvals)) - 1\).
- Returns
- boolWhether there are at least n_bvals different b-values in the
- gradient table used.
disperse_charges¶
-
dipy.core.gradients.
disperse_charges
(hemi, iters, const=0.2)¶ Models electrostatic repulsion on the unit sphere
Places charges on a sphere and simulates the repulsive forces felt by each one. Allows the charges to move for some number of iterations and returns their final location as well as the total potential of the system at each step.
- Parameters
- hemiHemiSphere
Points on a unit sphere.
- itersint
Number of iterations to run.
- constfloat
Using a smaller const could provide a more accurate result, but will need more iterations to converge.
- Returns
- hemiHemiSphere
Distributed points on a unit sphere.
- potentialndarray
The electrostatic potential at each iteration. This can be useful to check if the repulsion converged to a minimum.
Notes
This function is meant to be used with diffusion imaging so antipodal symmetry is assumed. Therefor each charge must not only be unique, but if there is a charge at +x, there cannot be a charge at -x. These are treated as the same location and because the distance between the two charges will be zero, the result will be unstable.
generate_bvecs¶
-
dipy.core.gradients.
generate_bvecs
(N, iters=5000)¶ Generates N bvectors.
Uses dipy.core.sphere.disperse_charges to model electrostatic repulsion on a unit sphere.
- Parameters
- Nint
The number of bvectors to generate. This should be equal to the number of bvals used.
- itersint
Number of iterations to run.
- Returns
- bvecs(N,3) ndarray
The generated directions, represented as a unit vector, of each gradient.
gradient_table¶
-
dipy.core.gradients.
gradient_table
(bvals, bvecs=None, big_delta=None, small_delta=None, b0_threshold=50, atol=0.01)¶ A general function for creating diffusion MR gradients.
It reads, loads and prepares scanner parameters like the b-values and b-vectors so that they can be useful during the reconstruction process.
- Parameters
- bvalscan be any of the four options
an array of shape (N,) or (1, N) or (N, 1) with the b-values.
a path for the file which contains an array like the above (1).
an array of shape (N, 4) or (4, N). Then this parameter is considered to be a b-table which contains both bvals and bvecs. In this case the next parameter is skipped.
a path for the file which contains an array like the one at (3).
- bvecscan be any of two options
an array of shape (N, 3) or (3, N) with the b-vectors.
a path for the file which contains an array like the previous.
- big_deltafloat
acquisition pulse separation time in seconds (default None)
- small_deltafloat
acquisition pulse duration time in seconds (default None)
- b0_thresholdfloat
All b-values with values less than or equal to bo_threshold are considered as b0s i.e. without diffusion weighting.
- atolfloat
All b-vectors need to be unit vectors up to a tolerance.
- Returns
- gradientsGradientTable
A GradientTable with all the gradient information.
Notes
Often b0s (b-values which correspond to images without diffusion weighting) have 0 values however in some cases the scanner cannot provide b0s of an exact 0 value and it gives a bit higher values e.g. 6 or 12. This is the purpose of the b0_threshold in the __init__.
We assume that the minimum number of b-values is 7.
B-vectors should be unit vectors.
Examples
>>> from dipy.core.gradients import gradient_table >>> bvals = 1500 * np.ones(7) >>> bvals[0] = 0 >>> sq2 = np.sqrt(2) / 2 >>> bvecs = np.array([[0, 0, 0], ... [1, 0, 0], ... [0, 1, 0], ... [0, 0, 1], ... [sq2, sq2, 0], ... [sq2, 0, sq2], ... [0, sq2, sq2]]) >>> gt = gradient_table(bvals, bvecs) >>> gt.bvecs.shape == bvecs.shape True >>> gt = gradient_table(bvals, bvecs.T) >>> gt.bvecs.shape == bvecs.T.shape False
gradient_table_from_bvals_bvecs¶
-
dipy.core.gradients.
gradient_table_from_bvals_bvecs
(bvals, bvecs, b0_threshold=50, atol=0.01, **kwargs)¶ Creates a GradientTable from a bvals array and a bvecs array
- Parameters
- bvalsarray_like (N,)
The b-value, or magnitude, of each gradient direction.
- bvecsarray_like (N, 3)
The direction, represented as a unit vector, of each gradient.
- b0_thresholdfloat
Gradients with b-value less than or equal to bo_threshold are considered to not have diffusion weighting.
- atolfloat
Each vector in bvecs must be a unit vectors up to a tolerance of atol.
- Returns
- gradientsGradientTable
A GradientTable with all the gradient information.
- Other Parameters
- **kwargsdict
Other keyword inputs are passed to GradientTable.
See also
gradient_table_from_gradient_strength_bvecs¶
-
dipy.core.gradients.
gradient_table_from_gradient_strength_bvecs
(gradient_strength, bvecs, big_delta, small_delta, b0_threshold=50, atol=0.01)¶ A general function for creating diffusion MR gradients.
It reads, loads and prepares scanner parameters like the b-values and b-vectors so that they can be useful during the reconstruction process.
- Parameters
- gradient_strengthan array of shape (N,),
gradient strength given in T/mm
- bvecscan be any of two options
an array of shape (N, 3) or (3, N) with the b-vectors.
a path for the file which contains an array like the previous.
- big_deltafloat or array of shape (N,)
acquisition pulse separation time in seconds
- small_deltafloat
acquisition pulse duration time in seconds
- b0_thresholdfloat
All b-values with values less than or equal to bo_threshold are considered as b0s i.e. without diffusion weighting.
- atolfloat
All b-vectors need to be unit vectors up to a tolerance.
- Returns
- gradientsGradientTable
A GradientTable with all the gradient information.
Notes
Often b0s (b-values which correspond to images without diffusion weighting) have 0 values however in some cases the scanner cannot provide b0s of an exact 0 value and it gives a bit higher values e.g. 6 or 12. This is the purpose of the b0_threshold in the __init__.
We assume that the minimum number of b-values is 7.
B-vectors should be unit vectors.
Examples
>>> from dipy.core.gradients import ( ... gradient_table_from_gradient_strength_bvecs) >>> gradient_strength = .03e-3 * np.ones(7) # clinical strength at 30 mT/m >>> big_delta = .03 # pulse separation of 30ms >>> small_delta = 0.01 # pulse duration of 10ms >>> gradient_strength[0] = 0 >>> sq2 = np.sqrt(2) / 2 >>> bvecs = np.array([[0, 0, 0], ... [1, 0, 0], ... [0, 1, 0], ... [0, 0, 1], ... [sq2, sq2, 0], ... [sq2, 0, sq2], ... [0, sq2, sq2]]) >>> gt = gradient_table_from_gradient_strength_bvecs( ... gradient_strength, bvecs, big_delta, small_delta)
gradient_table_from_qvals_bvecs¶
-
dipy.core.gradients.
gradient_table_from_qvals_bvecs
(qvals, bvecs, big_delta, small_delta, b0_threshold=50, atol=0.01)¶ A general function for creating diffusion MR gradients.
It reads, loads and prepares scanner parameters like the b-values and b-vectors so that they can be useful during the reconstruction process.
- Parameters
- qvalsan array of shape (N,),
q-value given in 1/mm
- bvecscan be any of two options
an array of shape (N, 3) or (3, N) with the b-vectors.
a path for the file which contains an array like the previous.
- big_deltafloat or array of shape (N,)
acquisition pulse separation time in seconds
- small_deltafloat
acquisition pulse duration time in seconds
- b0_thresholdfloat
All b-values with values less than or equal to bo_threshold are considered as b0s i.e. without diffusion weighting.
- atolfloat
All b-vectors need to be unit vectors up to a tolerance.
- Returns
- gradientsGradientTable
A GradientTable with all the gradient information.
Notes
Often b0s (b-values which correspond to images without diffusion weighting) have 0 values however in some cases the scanner cannot provide b0s of an exact 0 value and it gives a bit higher values e.g. 6 or 12. This is the purpose of the b0_threshold in the __init__.
We assume that the minimum number of b-values is 7.
B-vectors should be unit vectors.
Examples
>>> from dipy.core.gradients import gradient_table_from_qvals_bvecs >>> qvals = 30. * np.ones(7) >>> big_delta = .03 # pulse separation of 30ms >>> small_delta = 0.01 # pulse duration of 10ms >>> qvals[0] = 0 >>> sq2 = np.sqrt(2) / 2 >>> bvecs = np.array([[0, 0, 0], ... [1, 0, 0], ... [0, 1, 0], ... [0, 0, 1], ... [sq2, sq2, 0], ... [sq2, 0, sq2], ... [0, sq2, sq2]]) >>> gt = gradient_table_from_qvals_bvecs(qvals, bvecs, ... big_delta, small_delta)
inv¶
-
dipy.core.gradients.
inv
(a, overwrite_a=False, check_finite=True)¶ Compute the inverse of a matrix.
- Parameters
- aarray_like
Square matrix to be inverted.
- overwrite_abool, optional
Discard data in a (may improve performance). Default is False.
- check_finitebool, optional
Whether to check that the input matrix contains only finite numbers. Disabling may give a performance gain, but may result in problems (crashes, non-termination) if the inputs do contain infinities or NaNs.
- Returns
- ainvndarray
Inverse of the matrix a.
- Raises
- LinAlgError
If a is singular.
- ValueError
If a is not square, or not 2-dimensional.
Examples
>>> from scipy import linalg >>> a = np.array([[1., 2.], [3., 4.]]) >>> linalg.inv(a) array([[-2. , 1. ], [ 1.5, -0.5]]) >>> np.dot(a, linalg.inv(a)) array([[ 1., 0.], [ 0., 1.]])
polar¶
-
dipy.core.gradients.
polar
(a, side='right')¶ Compute the polar decomposition.
Returns the factors of the polar decomposition [1] u and p such that
a = up
(if side is “right”) ora = pu
(if side is “left”), where p is positive semidefinite. Depending on the shape of a, either the rows or columns of u are orthonormal. When a is a square array, u is a square unitary array. When a is not square, the “canonical polar decomposition” [2] is computed.- Parameters
- a(m, n) array_like
The array to be factored.
- side{‘left’, ‘right’}, optional
Determines whether a right or left polar decomposition is computed. If side is “right”, then
a = up
. If side is “left”, thena = pu
. The default is “right”.
- Returns
- u(m, n) ndarray
If a is square, then u is unitary. If m > n, then the columns of a are orthonormal, and if m < n, then the rows of u are orthonormal.
- pndarray
p is Hermitian positive semidefinite. If a is nonsingular, p is positive definite. The shape of p is (n, n) or (m, m), depending on whether side is “right” or “left”, respectively.
References
- 1(1,2)
R. A. Horn and C. R. Johnson, “Matrix Analysis”, Cambridge University Press, 1985.
- 2(1,2)
N. J. Higham, “Functions of Matrices: Theory and Computation”, SIAM, 2008.
Examples
>>> from scipy.linalg import polar >>> a = np.array([[1, -1], [2, 4]]) >>> u, p = polar(a) >>> u array([[ 0.85749293, -0.51449576], [ 0.51449576, 0.85749293]]) >>> p array([[ 1.88648444, 1.2004901 ], [ 1.2004901 , 3.94446746]])
A non-square example, with m < n:
>>> b = np.array([[0.5, 1, 2], [1.5, 3, 4]]) >>> u, p = polar(b) >>> u array([[-0.21196618, -0.42393237, 0.88054056], [ 0.39378971, 0.78757942, 0.4739708 ]]) >>> p array([[ 0.48470147, 0.96940295, 1.15122648], [ 0.96940295, 1.9388059 , 2.30245295], [ 1.15122648, 2.30245295, 3.65696431]]) >>> u.dot(p) # Verify the decomposition. array([[ 0.5, 1. , 2. ], [ 1.5, 3. , 4. ]]) >>> u.dot(u.T) # The rows of u are orthonormal. array([[ 1.00000000e+00, -2.07353665e-17], [ -2.07353665e-17, 1.00000000e+00]])
Another non-square example, with m > n:
>>> c = b.T >>> u, p = polar(c) >>> u array([[-0.21196618, 0.39378971], [-0.42393237, 0.78757942], [ 0.88054056, 0.4739708 ]]) >>> p array([[ 1.23116567, 1.93241587], [ 1.93241587, 4.84930602]]) >>> u.dot(p) # Verify the decomposition. array([[ 0.5, 1.5], [ 1. , 3. ], [ 2. , 4. ]]) >>> u.T.dot(u) # The columns of u are orthonormal. array([[ 1.00000000e+00, -1.26363763e-16], [ -1.26363763e-16, 1.00000000e+00]])
reorient_bvecs¶
-
dipy.core.gradients.
reorient_bvecs
(gtab, affines)¶ Reorient the directions in a GradientTable.
When correcting for motion, rotation of the diffusion-weighted volumes might cause systematic bias in rotationally invariant measures, such as FA and MD, and also cause characteristic biases in tractography, unless the gradient directions are appropriately reoriented to compensate for this effect [Leemans2009].
- Parameters
- gtabGradientTable
The nominal gradient table with which the data were acquired.
- affineslist or ndarray of shape (n, 4, 4) or (n, 3, 3)
Each entry in this list or array contain either an affine transformation (4,4) or a rotation matrix (3, 3). In both cases, the transformations encode the rotation that was applied to the image corresponding to one of the non-zero gradient directions (ordered according to their order in gtab.bvecs[~gtab.b0s_mask])
- Returns
- gtaba GradientTable class instance with the reoriented directions
References
round_bvals¶
-
dipy.core.gradients.
round_bvals
(bvals, bmag=None)¶ “This function rounds the b-values
- Parameters
- bvalsndarray
Array containing the b-values
- bmagint
The order of magnitude to round the b-values. If not given b-values will be rounded relative to the order of magnitude \(bmag = (bmagmax - 1)\), where bmaxmag is the magnitude order of the larger b-value.
- Returns
- ——
- rbvalsndarray
Array containing the rounded b-values
unique_bvals¶
-
dipy.core.gradients.
unique_bvals
(bvals, bmag=None, rbvals=False)¶ This function gives the unique rounded b-values of the data
- Parameters
- bvalsndarray
Array containing the b-values
- bmagint
The order of magnitude that the bvalues have to differ to be considered an unique b-value. B-values are also rounded up to this order of magnitude. Default: derive this value from the maximal b-value provided: \(bmag=log_{10}(max(bvals)) - 1\).
- rbvalsbool, optional
If True function also returns all individual rounded b-values. Default: False
- Returns
- ——
- ubvalsndarray
Array containing the rounded unique b-values
vector_norm¶
-
dipy.core.gradients.
vector_norm
(vec, axis=-1, keepdims=False)¶ Return vector Euclidean (L2) norm
See unit vector and Euclidean norm
- Parameters
- vecarray_like
Vectors to norm.
- axisint
Axis over which to norm. By default norm over last axis. If axis is None, vec is flattened then normed.
- keepdimsbool
If True, the output will have the same number of dimensions as vec, with shape 1 on axis.
- Returns
- normarray
Euclidean norms of vectors.
Examples
>>> import numpy as np >>> vec = [[8, 15, 0], [0, 36, 77]] >>> vector_norm(vec) array([ 17., 85.]) >>> vector_norm(vec, keepdims=True) array([[ 17.], [ 85.]]) >>> vector_norm(vec, axis=0) array([ 8., 39., 77.])
Graph
¶
-
class
dipy.core.graph.
Graph
¶ Bases:
object
A simple graph class
Methods
add_edge
add_node
all_paths
children
del_node
del_node_and_edges
down
down_short
parents
shortest_path
up
up_short
-
__init__
()¶ A graph class with nodes and edges :-)
This class allows us to:
find the shortest path
find all paths
add/delete nodes and edges
get parent & children nodes
Examples
>>> from dipy.core.graph import Graph >>> g=Graph() >>> g.add_node('a',5) >>> g.add_node('b',6) >>> g.add_node('c',10) >>> g.add_node('d',11) >>> g.add_edge('a','b') >>> g.add_edge('b','c') >>> g.add_edge('c','d') >>> g.add_edge('b','d') >>> g.up_short('d') ['d', 'b', 'a']
-
add_edge
(n, m, ws=True, wp=True)¶
-
add_node
(n, attr=None)¶
-
all_paths
(graph, start, end=None, path=[])¶
-
children
(n)¶
-
del_node
(n)¶
-
del_node_and_edges
(n)¶
-
down
(n)¶
-
down_short
(n)¶
-
parents
(n)¶
-
shortest_path
(graph, start, end=None, path=[])¶
-
up
(n)¶
-
up_short
(n)¶
-
histeq¶
-
dipy.core.histeq.
histeq
(arr, num_bins=256)¶ Performs an histogram equalization on
arr
. This was taken from: http://www.janeriksolem.net/2009/06/histogram-equalization-with-python-and.html- Parameters
- arrndarray
Image on which to perform histogram equalization.
- num_binsint
Number of bins used to construct the histogram.
- Returns
- resultndarray
Histogram equalized image.
as_strided¶
-
dipy.core.ndindex.
as_strided
(x, shape=None, strides=None, subok=False, writeable=True)¶ Create a view into the array with the given shape and strides.
Warning
This function has to be used with extreme care, see notes.
- Parameters
- xndarray
Array to create a new.
- shapesequence of int, optional
The shape of the new array. Defaults to
x.shape
.- stridessequence of int, optional
The strides of the new array. Defaults to
x.strides
.- subokbool, optional
New in version 1.10.
If True, subclasses are preserved.
- writeablebool, optional
New in version 1.12.
If set to False, the returned array will always be readonly. Otherwise it will be writable if the original array was. It is advisable to set this to False if possible (see Notes).
- Returns
- viewndarray
See also
broadcast_to
broadcast an array to a given shape.
reshape
reshape an array.
Notes
as_strided
creates a view into the array given the exact strides and shape. This means it manipulates the internal data structure of ndarray and, if done incorrectly, the array elements can point to invalid memory and can corrupt results or crash your program. It is advisable to always use the originalx.strides
when calculating new strides to avoid reliance on a contiguous memory layout.Furthermore, arrays created with this function often contain self overlapping memory, so that two elements are identical. Vectorized write operations on such arrays will typically be unpredictable. They may even give different results for small, large, or transposed arrays. Since writing to these arrays has to be tested and done with great care, you may want to use
writeable=False
to avoid accidental write operations.For these reasons it is advisable to avoid
as_strided
when possible.
ndindex¶
-
dipy.core.ndindex.
ndindex
(shape)¶ An N-dimensional iterator object to index arrays.
Given the shape of an array, an ndindex instance iterates over the N-dimensional index of the array. At each iteration a tuple of indices is returned; the last dimension is iterated over first.
- Parameters
- shapetuple of ints
The dimensions of the array.
Examples
>>> from dipy.core.ndindex import ndindex >>> shape = (3, 2, 1) >>> for index in ndindex(shape): ... print(index) (0, 0, 0) (0, 1, 0) (1, 0, 0) (1, 1, 0) (2, 0, 0) (2, 1, 0)
OneTimeProperty
¶
-
class
dipy.core.onetime.
OneTimeProperty
(func)¶ Bases:
object
A descriptor to make special properties that become normal attributes.
This is meant to be used mostly by the auto_attr decorator in this module.
-
__init__
(func)¶ Create a OneTimeProperty instance.
- Parameters
- funcmethod
The method that will be called the first time to compute a value. Afterwards, the method’s name will be a standard attribute holding the value of this computation.
-
ResetMixin
¶
-
class
dipy.core.onetime.
ResetMixin
¶ Bases:
object
A Mixin class to add a .reset() method to users of OneTimeProperty.
By default, auto attributes once computed, become static. If they happen to depend on other parts of an object and those parts change, their values may now be invalid.
This class offers a .reset() method that users can call explicitly when they know the state of their objects may have changed and they want to ensure that all their special attributes should be invalidated. Once reset() is called, all their auto attributes are reset to their OneTimeProperty descriptors, and their accessor functions will be triggered again.
Warning
If a class has a set of attributes that are OneTimeProperty, but that can be initialized from any one of them, do NOT use this mixin! For instance, UniformTimeSeries can be initialized with only sampling_rate and t0, sampling_interval and time are auto-computed. But if you were to reset() a UniformTimeSeries, it would lose all 4, and there would be then no way to break the circular dependency chains.
If this becomes a problem in practice (for our analyzer objects it isn’t, as they don’t have the above pattern), we can extend reset() to check for a _no_reset set of names in the instance which are meant to be kept protected. But for now this is NOT done, so caveat emptor.
Examples
>>> class A(ResetMixin): ... def __init__(self,x=1.0): ... self.x = x ... ... @auto_attr ... def y(self): ... print('*** y computation executed ***') ... return self.x / 2.0 ...
>>> a = A(10)
About to access y twice, the second time no computation is done: >>> a.y * y computation executed * 5.0 >>> a.y 5.0
Changing x >>> a.x = 20
a.y doesn’t change to 10, since it is a static attribute: >>> a.y 5.0
We now reset a, and this will then force all auto attributes to recompute the next time we access them: >>> a.reset()
About to access y twice again after reset(): >>> a.y * y computation executed * 10.0 >>> a.y 10.0
Methods
reset
()Reset all OneTimeProperty attributes that may have fired already.
-
__init__
($self, /, *args, **kwargs)¶ Initialize self. See help(type(self)) for accurate signature.
-
reset
()¶ Reset all OneTimeProperty attributes that may have fired already.
-
auto_attr¶
-
dipy.core.onetime.
auto_attr
(func)¶ Decorator to create OneTimeProperty attributes.
- Parameters
- funcmethod
The method that will be called the first time to compute a value. Afterwards, the method’s name will be a standard attribute holding the value of this computation.
Examples
>>> class MagicProp(object): ... @auto_attr ... def a(self): ... return 99 ... >>> x = MagicProp() >>> 'a' in x.__dict__ False >>> x.a 99 >>> 'a' in x.__dict__ True
NonNegativeLeastSquares
¶
-
class
dipy.core.optimize.
NonNegativeLeastSquares
(*args, **kwargs)¶ Bases:
dipy.core.optimize.SKLearnLinearSolver
A sklearn-like interface to scipy.optimize.nnls
Methods
fit
(X, y)Fit the NonNegativeLeastSquares linear model to data
predict
(X)Predict using the result of the model
-
__init__
(*args, **kwargs)¶ Initialize self. See help(type(self)) for accurate signature.
-
fit
(X, y)¶ Fit the NonNegativeLeastSquares linear model to data
-
Optimizer
¶
-
class
dipy.core.optimize.
Optimizer
(fun, x0, args=(), method='L-BFGS-B', jac=None, hess=None, hessp=None, bounds=None, constraints=(), tol=None, callback=None, options=None, evolution=False)¶ Bases:
object
- Attributes
- evolution
- fopt
- message
- nfev
- nit
- xopt
Methods
print_summary
-
__init__
(fun, x0, args=(), method='L-BFGS-B', jac=None, hess=None, hessp=None, bounds=None, constraints=(), tol=None, callback=None, options=None, evolution=False)¶ A class for handling minimization of scalar function of one or more variables.
- Parameters
- funcallable
Objective function.
- x0ndarray
Initial guess.
- argstuple, optional
Extra arguments passed to the objective function and its derivatives (Jacobian, Hessian).
- methodstr, optional
Type of solver. Should be one of
‘Nelder-Mead’
‘Powell’
‘CG’
‘BFGS’
‘Newton-CG’
‘Anneal’
‘L-BFGS-B’
‘TNC’
‘COBYLA’
‘SLSQP’
‘dogleg’
‘trust-ncg’
- jacbool or callable, optional
Jacobian of objective function. Only for CG, BFGS, Newton-CG, dogleg, trust-ncg. If jac is a Boolean and is True, fun is assumed to return the value of Jacobian along with the objective function. If False, the Jacobian will be estimated numerically. jac can also be a callable returning the Jacobian of the objective. In this case, it must accept the same arguments as fun.
- hess, hesspcallable, optional
Hessian of objective function or Hessian of objective function times an arbitrary vector p. Only for Newton-CG, dogleg, trust-ncg. Only one of hessp or hess needs to be given. If hess is provided, then hessp will be ignored. If neither hess nor hessp is provided, then the hessian product will be approximated using finite differences on jac. hessp must compute the Hessian times an arbitrary vector.
- boundssequence, optional
Bounds for variables (only for L-BFGS-B, TNC and SLSQP).
(min, max)
pairs for each element inx
, defining the bounds on that parameter. Use None for one ofmin
ormax
when there is no bound in that direction.- constraintsdict or sequence of dict, optional
Constraints definition (only for COBYLA and SLSQP). Each constraint is defined in a dictionary with fields:
- typestr
Constraint type: ‘eq’ for equality, ‘ineq’ for inequality.
- funcallable
The function defining the constraint.
- jaccallable, optional
The Jacobian of fun (only for SLSQP).
- argssequence, optional
Extra arguments to be passed to the function and Jacobian.
Equality constraint means that the constraint function result is to be zero whereas inequality means that it is to be non-negative. Note that COBYLA only supports inequality constraints.
- tolfloat, optional
Tolerance for termination. For detailed control, use solver-specific options.
- callbackcallable, optional
Called after each iteration, as
callback(xk)
, wherexk
is the current parameter vector. Only available using Scipy >= 0.12.- optionsdict, optional
A dictionary of solver options. All methods accept the following generic options:
- maxiterint
Maximum number of iterations to perform.
- dispbool
Set to True to print convergence messages.
For method-specific options, see show_options(‘minimize’, method).
- evolutionbool, optional
save history of x for each iteration. Only available using Scipy >= 0.12.
See also
scipy.optimize.minimize
-
property
evolution
¶
-
property
fopt
¶
-
property
message
¶
-
property
nfev
¶
-
property
nit
¶
-
print_summary
()¶
-
property
xopt
¶
SKLearnLinearSolver
¶
-
class
dipy.core.optimize.
SKLearnLinearSolver
(*args, **kwargs)¶ Bases:
object
Provide a sklearn-like uniform interface to algorithms that solve problems of the form: \(y = Ax\) for \(x\)
Sub-classes of SKLearnLinearSolver should provide a ‘fit’ method that have the following signature: SKLearnLinearSolver.fit(X, y), which would set an attribute SKLearnLinearSolver.coef_, with the shape (X.shape[1],), such that an estimate of y can be calculated as: y_hat = np.dot(X, SKLearnLinearSolver.coef_.T)
Methods
fit
(X, y)Implement for all derived classes
predict
(X)Predict using the result of the model
-
__init__
(*args, **kwargs)¶ Initialize self. See help(type(self)) for accurate signature.
-
abstract
fit
(X, y)¶ Implement for all derived classes
-
predict
(X)¶ Predict using the result of the model
- Parameters
- Xarray-like (n_samples, n_features)
Samples.
- Returns
- Carray, shape = (n_samples,)
Predicted values.
-
minimize¶
-
dipy.core.optimize.
minimize
(fun, x0, args=(), method=None, jac=None, hess=None, hessp=None, bounds=None, constraints=(), tol=None, callback=None, options=None)¶ Minimization of scalar function of one or more variables.
- Parameters
- funcallable
The objective function to be minimized.
fun(x, *args) -> float
where x is an 1-D array with shape (n,) and args is a tuple of the fixed parameters needed to completely specify the function.
- x0ndarray, shape (n,)
Initial guess. Array of real elements of size (n,), where ‘n’ is the number of independent variables.
- argstuple, optional
Extra arguments passed to the objective function and its derivatives (fun, jac and hess functions).
- methodstr or callable, optional
Type of solver. Should be one of
‘Nelder-Mead’ (see here)
‘Powell’ (see here)
‘CG’ (see here)
‘BFGS’ (see here)
‘Newton-CG’ (see here)
‘L-BFGS-B’ (see here)
‘TNC’ (see here)
‘COBYLA’ (see here)
‘SLSQP’ (see here)
‘trust-constr’(see here)
‘dogleg’ (see here)
‘trust-ncg’ (see here)
‘trust-exact’ (see here)
‘trust-krylov’ (see here)
custom - a callable object (added in version 0.14.0), see below for description.
If not given, chosen to be one of
BFGS
,L-BFGS-B
,SLSQP
, depending if the problem has constraints or bounds.- jac{callable, ‘2-point’, ‘3-point’, ‘cs’, bool}, optional
Method for computing the gradient vector. Only for CG, BFGS, Newton-CG, L-BFGS-B, TNC, SLSQP, dogleg, trust-ncg, trust-krylov, trust-exact and trust-constr. If it is a callable, it should be a function that returns the gradient vector:
jac(x, *args) -> array_like, shape (n,)
where x is an array with shape (n,) and args is a tuple with the fixed parameters. Alternatively, the keywords {‘2-point’, ‘3-point’, ‘cs’} select a finite difference scheme for numerical estimation of the gradient. Options ‘3-point’ and ‘cs’ are available only to ‘trust-constr’. If jac is a Boolean and is True, fun is assumed to return the gradient along with the objective function. If False, the gradient will be estimated using ‘2-point’ finite difference estimation.
- hess{callable, ‘2-point’, ‘3-point’, ‘cs’, HessianUpdateStrategy}, optional
Method for computing the Hessian matrix. Only for Newton-CG, dogleg, trust-ncg, trust-krylov, trust-exact and trust-constr. If it is callable, it should return the Hessian matrix:
hess(x, *args) -> {LinearOperator, spmatrix, array}, (n, n)
where x is a (n,) ndarray and args is a tuple with the fixed parameters. LinearOperator and sparse matrix returns are allowed only for ‘trust-constr’ method. Alternatively, the keywords {‘2-point’, ‘3-point’, ‘cs’} select a finite difference scheme for numerical estimation. Or, objects implementing HessianUpdateStrategy interface can be used to approximate the Hessian. Available quasi-Newton methods implementing this interface are:
BFGS;
SR1.
Whenever the gradient is estimated via finite-differences, the Hessian cannot be estimated with options {‘2-point’, ‘3-point’, ‘cs’} and needs to be estimated using one of the quasi-Newton strategies. Finite-difference options {‘2-point’, ‘3-point’, ‘cs’} and HessianUpdateStrategy are available only for ‘trust-constr’ method.
- hesspcallable, optional
Hessian of objective function times an arbitrary vector p. Only for Newton-CG, trust-ncg, trust-krylov, trust-constr. Only one of hessp or hess needs to be given. If hess is provided, then hessp will be ignored. hessp must compute the Hessian times an arbitrary vector:
hessp(x, p, *args) -> ndarray shape (n,)
where x is a (n,) ndarray, p is an arbitrary vector with dimension (n,) and args is a tuple with the fixed parameters.
- boundssequence or Bounds, optional
Bounds on variables for L-BFGS-B, TNC, SLSQP and trust-constr methods. There are two ways to specify the bounds:
Instance of Bounds class.
Sequence of
(min, max)
pairs for each element in x. None is used to specify no bound.
- constraints{Constraint, dict} or List of {Constraint, dict}, optional
Constraints definition (only for COBYLA, SLSQP and trust-constr). Constraints for ‘trust-constr’ are defined as a single object or a list of objects specifying constraints to the optimization problem. Available constraints are:
LinearConstraint
NonlinearConstraint
Constraints for COBYLA, SLSQP are defined as a list of dictionaries. Each dictionary with fields:
- typestr
Constraint type: ‘eq’ for equality, ‘ineq’ for inequality.
- funcallable
The function defining the constraint.
- jaccallable, optional
The Jacobian of fun (only for SLSQP).
- argssequence, optional
Extra arguments to be passed to the function and Jacobian.
Equality constraint means that the constraint function result is to be zero whereas inequality means that it is to be non-negative. Note that COBYLA only supports inequality constraints.
- tolfloat, optional
Tolerance for termination. For detailed control, use solver-specific options.
- optionsdict, optional
A dictionary of solver options. All methods accept the following generic options:
- maxiterint
Maximum number of iterations to perform.
- dispbool
Set to True to print convergence messages.
For method-specific options, see
show_options()
.- callbackcallable, optional
Called after each iteration. For ‘trust-constr’ it is a callable with the signature:
callback(xk, OptimizeResult state) -> bool
where
xk
is the current parameter vector. andstate
is an OptimizeResult object, with the same fields as the ones from the return. If callback returns True the algorithm execution is terminated. For all the other methods, the signature is:callback(xk)
where
xk
is the current parameter vector.
- Returns
- resOptimizeResult
The optimization result represented as a
OptimizeResult
object. Important attributes are:x
the solution array,success
a Boolean flag indicating if the optimizer exited successfully andmessage
which describes the cause of the termination. See OptimizeResult for a description of other attributes.
See also
minimize_scalar
Interface to minimization algorithms for scalar univariate functions
show_options
Additional options accepted by the solvers
Notes
This section describes the available solvers that can be selected by the ‘method’ parameter. The default method is BFGS.
Unconstrained minimization
Method Nelder-Mead uses the Simplex algorithm [1], [2]. This algorithm is robust in many applications. However, if numerical computation of derivative can be trusted, other algorithms using the first and/or second derivatives information might be preferred for their better performance in general.
Method Powell is a modification of Powell’s method [3], [4] which is a conjugate direction method. It performs sequential one-dimensional minimizations along each vector of the directions set (direc field in options and info), which is updated at each iteration of the main minimization loop. The function need not be differentiable, and no derivatives are taken.
Method CG uses a nonlinear conjugate gradient algorithm by Polak and Ribiere, a variant of the Fletcher-Reeves method described in [5] pp. 120-122. Only the first derivatives are used.
Method BFGS uses the quasi-Newton method of Broyden, Fletcher, Goldfarb, and Shanno (BFGS) [5] pp. 136. It uses the first derivatives only. BFGS has proven good performance even for non-smooth optimizations. This method also returns an approximation of the Hessian inverse, stored as hess_inv in the OptimizeResult object.
Method Newton-CG uses a Newton-CG algorithm [5] pp. 168 (also known as the truncated Newton method). It uses a CG method to the compute the search direction. See also TNC method for a box-constrained minimization with a similar algorithm. Suitable for large-scale problems.
Method dogleg uses the dog-leg trust-region algorithm [5] for unconstrained minimization. This algorithm requires the gradient and Hessian; furthermore the Hessian is required to be positive definite.
Method trust-ncg uses the Newton conjugate gradient trust-region algorithm [5] for unconstrained minimization. This algorithm requires the gradient and either the Hessian or a function that computes the product of the Hessian with a given vector. Suitable for large-scale problems.
Method trust-krylov uses the Newton GLTR trust-region algorithm [14], [15] for unconstrained minimization. This algorithm requires the gradient and either the Hessian or a function that computes the product of the Hessian with a given vector. Suitable for large-scale problems. On indefinite problems it requires usually less iterations than the trust-ncg method and is recommended for medium and large-scale problems.
Method trust-exact is a trust-region method for unconstrained minimization in which quadratic subproblems are solved almost exactly [13]. This algorithm requires the gradient and the Hessian (which is not required to be positive definite). It is, in many situations, the Newton method to converge in fewer iteraction and the most recommended for small and medium-size problems.
Bound-Constrained minimization
Method L-BFGS-B uses the L-BFGS-B algorithm [6], [7] for bound constrained minimization.
Method TNC uses a truncated Newton algorithm [5], [8] to minimize a function with variables subject to bounds. This algorithm uses gradient information; it is also called Newton Conjugate-Gradient. It differs from the Newton-CG method described above as it wraps a C implementation and allows each variable to be given upper and lower bounds.
Constrained Minimization
Method COBYLA uses the Constrained Optimization BY Linear Approximation (COBYLA) method [9], [10], [11]. The algorithm is based on linear approximations to the objective function and each constraint. The method wraps a FORTRAN implementation of the algorithm. The constraints functions ‘fun’ may return either a single number or an array or list of numbers.
Method SLSQP uses Sequential Least SQuares Programming to minimize a function of several variables with any combination of bounds, equality and inequality constraints. The method wraps the SLSQP Optimization subroutine originally implemented by Dieter Kraft [12]. Note that the wrapper handles infinite values in bounds by converting them into large floating values.
Method trust-constr is a trust-region algorithm for constrained optimization. It swiches between two implementations depending on the problem definition. It is the most versatile constrained minimization algorithm implemented in SciPy and the most appropriate for large-scale problems. For equality constrained problems it is an implementation of Byrd-Omojokun Trust-Region SQP method described in [17] and in [5], p. 549. When inequality constraints are imposed as well, it swiches to the trust-region interior point method described in [16]. This interior point algorithm, in turn, solves inequality constraints by introducing slack variables and solving a sequence of equality-constrained barrier problems for progressively smaller values of the barrier parameter. The previously described equality constrained SQP method is used to solve the subproblems with increasing levels of accuracy as the iterate gets closer to a solution.
Finite-Difference Options
For Method trust-constr the gradient and the Hessian may be approximated using three finite-difference schemes: {‘2-point’, ‘3-point’, ‘cs’}. The scheme ‘cs’ is, potentially, the most accurate but it requires the function to correctly handles complex inputs and to be differentiable in the complex plane. The scheme ‘3-point’ is more accurate than ‘2-point’ but requires twice as much operations.
Custom minimizers
It may be useful to pass a custom minimization method, for example when using a frontend to this method such as scipy.optimize.basinhopping or a different library. You can simply pass a callable as the
method
parameter.The callable is called as
method(fun, x0, args, **kwargs, **options)
wherekwargs
corresponds to any other parameters passed to minimize (such as callback, hess, etc.), except the options dict, which has its contents also passed as method parameters pair by pair. Also, if jac has been passed as a bool type, jac and fun are mangled so that fun returns just the function values and jac is converted to a function returning the Jacobian. The method shall return anOptimizeResult
object.The provided method callable must be able to accept (and possibly ignore) arbitrary parameters; the set of parameters accepted by minimize may expand in future versions and then these parameters will be passed to the method. You can find an example in the scipy.optimize tutorial.
New in version 0.11.0.
References
- 1(1,2)
Nelder, J A, and R Mead. 1965. A Simplex Method for Function Minimization. The Computer Journal 7: 308-13.
- 2(1,2)
Wright M H. 1996. Direct search methods: Once scorned, now respectable, in Numerical Analysis 1995: Proceedings of the 1995 Dundee Biennial Conference in Numerical Analysis (Eds. D F Griffiths and G A Watson). Addison Wesley Longman, Harlow, UK. 191-208.
- 3(1,2)
Powell, M J D. 1964. An efficient method for finding the minimum of a function of several variables without calculating derivatives. The Computer Journal 7: 155-162.
- 4(1,2)
Press W, S A Teukolsky, W T Vetterling and B P Flannery. Numerical Recipes (any edition), Cambridge University Press.
- 5(1,2,3,4,5,6,7,8,9)
Nocedal, J, and S J Wright. 2006. Numerical Optimization. Springer New York.
- 6(1,2)
Byrd, R H and P Lu and J. Nocedal. 1995. A Limited Memory Algorithm for Bound Constrained Optimization. SIAM Journal on Scientific and Statistical Computing 16 (5): 1190-1208.
- 7(1,2)
Zhu, C and R H Byrd and J Nocedal. 1997. L-BFGS-B: Algorithm 778: L-BFGS-B, FORTRAN routines for large scale bound constrained optimization. ACM Transactions on Mathematical Software 23 (4): 550-560.
- 8(1,2)
Nash, S G. Newton-Type Minimization Via the Lanczos Method. 1984. SIAM Journal of Numerical Analysis 21: 770-778.
- 9(1,2)
Powell, M J D. A direct search optimization method that models the objective and constraint functions by linear interpolation. 1994. Advances in Optimization and Numerical Analysis, eds. S. Gomez and J-P Hennart, Kluwer Academic (Dordrecht), 51-67.
- 10(1,2)
Powell M J D. Direct search algorithms for optimization calculations. 1998. Acta Numerica 7: 287-336.
- 11(1,2)
Powell M J D. A view of algorithms for optimization without derivatives. 2007.Cambridge University Technical Report DAMTP 2007/NA03
- 12(1,2)
Kraft, D. A software package for sequential quadratic programming. 1988. Tech. Rep. DFVLR-FB 88-28, DLR German Aerospace Center – Institute for Flight Mechanics, Koln, Germany.
- 13(1,2)
Conn, A. R., Gould, N. I., and Toint, P. L. Trust region methods. 2000. Siam. pp. 169-200.
- 14(1,2)
F. Lenders, C. Kirches, A. Potschka: “trlib: A vector-free implementation of the GLTR method for iterative solution of the trust region problem”, https://arxiv.org/abs/1611.04718
- 15(1,2)
N. Gould, S. Lucidi, M. Roma, P. Toint: “Solving the Trust-Region Subproblem using the Lanczos Method”, SIAM J. Optim., 9(2), 504–525, (1999).
- 16(1,2)
Byrd, Richard H., Mary E. Hribar, and Jorge Nocedal. 1999. An interior point algorithm for large-scale nonlinear programming. SIAM Journal on Optimization 9.4: 877-900.
- 17(1,2)
Lalee, Marucha, Jorge Nocedal, and Todd Plantega. 1998. On the implementation of an algorithm for large-scale equality constrained optimization. SIAM Journal on Optimization 8.3: 682-706.
Examples
Let us consider the problem of minimizing the Rosenbrock function. This function (and its respective derivatives) is implemented in rosen (resp. rosen_der, rosen_hess) in the scipy.optimize.
>>> from scipy.optimize import minimize, rosen, rosen_der
A simple application of the Nelder-Mead method is:
>>> x0 = [1.3, 0.7, 0.8, 1.9, 1.2] >>> res = minimize(rosen, x0, method='Nelder-Mead', tol=1e-6) >>> res.x array([ 1., 1., 1., 1., 1.])
Now using the BFGS algorithm, using the first derivative and a few options:
>>> res = minimize(rosen, x0, method='BFGS', jac=rosen_der, ... options={'gtol': 1e-6, 'disp': True}) Optimization terminated successfully. Current function value: 0.000000 Iterations: 26 Function evaluations: 31 Gradient evaluations: 31 >>> res.x array([ 1., 1., 1., 1., 1.]) >>> print(res.message) Optimization terminated successfully. >>> res.hess_inv array([[ 0.00749589, 0.01255155, 0.02396251, 0.04750988, 0.09495377], # may vary [ 0.01255155, 0.02510441, 0.04794055, 0.09502834, 0.18996269], [ 0.02396251, 0.04794055, 0.09631614, 0.19092151, 0.38165151], [ 0.04750988, 0.09502834, 0.19092151, 0.38341252, 0.7664427 ], [ 0.09495377, 0.18996269, 0.38165151, 0.7664427, 1.53713523]])
Next, consider a minimization problem with several constraints (namely Example 16.4 from [5]). The objective function is:
>>> fun = lambda x: (x[0] - 1)**2 + (x[1] - 2.5)**2
There are three constraints defined as:
>>> cons = ({'type': 'ineq', 'fun': lambda x: x[0] - 2 * x[1] + 2}, ... {'type': 'ineq', 'fun': lambda x: -x[0] - 2 * x[1] + 6}, ... {'type': 'ineq', 'fun': lambda x: -x[0] + 2 * x[1] + 2})
And variables must be positive, hence the following bounds:
>>> bnds = ((0, None), (0, None))
The optimization problem is solved using the SLSQP method as:
>>> res = minimize(fun, (2, 0), method='SLSQP', bounds=bnds, ... constraints=cons)
It should converge to the theoretical solution (1.4 ,1.7).
sparse_nnls¶
-
dipy.core.optimize.
sparse_nnls
(y, X, momentum=1, step_size=0.01, non_neg=True, check_error_iter=10, max_error_checks=10, converge_on_sse=0.99)¶ Solve y=Xh for h, using gradient descent, with X a sparse matrix.
- Parameters
- y1-d array of shape (N)
The data. Needs to be dense.
- Xndarray. May be either sparse or dense. Shape (N, M)
The regressors
- momentumfloat, optional (default: 1).
The persistence of the gradient.
- step_sizefloat, optional (default: 0.01).
The increment of parameter update in each iteration
- non_negBoolean, optional (default: True)
Whether to enforce non-negativity of the solution.
- check_error_iterint (default:10)
How many rounds to run between error evaluation for convergence-checking.
- max_error_checksint (default: 10)
Don’t check errors more than this number of times if no improvement in r-squared is seen.
- converge_on_ssefloat (default: 0.99)
a percentage improvement in SSE that is required each time to say that things are still going well.
- Returns
- h_bestThe best estimate of the parameters.
spdot¶
-
dipy.core.optimize.
spdot
(A, B)¶ The same as np.dot(A, B), except it works even if A or B or both are sparse matrices.
- Parameters
- A, Barrays of shape (m, n), (n, k)
- Returns
- The matrix product AB. If both A and B are sparse, the result will be a
- sparse matrix. Otherwise, a dense result is returned
- See discussion here:
- http://mail.scipy.org/pipermail/scipy-user/2010-November/027700.html
Profiler
¶
-
class
dipy.core.profile.
Profiler
(call=None, *args)¶ Bases:
object
Profile python/cython files or functions
If you are profiling cython code you need to add # cython: profile=True on the top of your .pyx file
and for the functions that you do not want to profile you can use this decorator in your cython files
@cython.profile(False)
- Parameters
- callerfile or function call
- argsfunction arguments
References
http://docs.cython.org/src/tutorial/profiling_tutorial.html http://docs.python.org/library/profile.html http://packages.python.org/line_profiler/
Examples
from dipy.core.profile import Profiler import numpy as np p=Profiler(np.sum,np.random.rand(1000000,3)) fname=’test.py’ p=Profiler(fname) p.print_stats(10) p.print_stats(‘det’)
- Attributes
- statsfunction, stats.print_stats(10) will prin the 10 slower functions
Methods
print_stats
([N])Print stats for profiling
-
__init__
(call=None, *args)¶ Initialize self. See help(type(self)) for accurate signature.
-
print_stats
(N=10)¶ Print stats for profiling
You can use it in all different ways developed in pstats for example print_stats(10) will give you the 10 slowest calls or print_stats(‘function_name’) will give you the stats for all the calls with name ‘function_name’
- Parameters
- Nstats.print_stats argument
optional_package¶
-
dipy.core.profile.
optional_package
(name, trip_msg=None)¶ Return package-like thing and module setup for package name
- Parameters
- namestr
package name
- trip_msgNone or str
message to give when someone tries to use the return package, but we could not import it, and have returned a TripWire object instead. Default message if None.
- Returns
- pkg_likemodule or
TripWire
instance If we can import the package, return it. Otherwise return an object raising an error when accessed
- have_pkgbool
True if import for package was successful, false otherwise
- module_setupfunction
callable usually set as
setup_module
in calling namespace, to allow skipping tests.
- pkg_likemodule or
Examples
Typical use would be something like this at the top of a module using an optional package:
>>> from dipy.utils.optpkg import optional_package >>> pkg, have_pkg, setup_module = optional_package('not_a_package')
Of course in this case the package doesn’t exist, and so, in the module:
>>> have_pkg False
and
>>> pkg.some_function() #doctest: +IGNORE_EXCEPTION_DETAIL Traceback (most recent call last): ... TripWireError: We need package not_a_package for these functions, but ``import not_a_package`` raised an ImportError
If the module does exist - we get the module
>>> pkg, _, _ = optional_package('os') >>> hasattr(pkg, 'path') True
Or a submodule if that’s what we asked for
>>> subpkg, _, _ = optional_package('os.path') >>> hasattr(subpkg, 'dirname') True
LEcuyer¶
-
dipy.core.rng.
LEcuyer
()¶ Generate uniformly distributed random numbers using the 32-bit generator from figure 3 of:
L’Ecuyer, P. Efficient and portable combined random number generators, C.A.C.M., vol. 31, 742-749 & 774-?, June 1988.
The cycle length is claimed to be 2.30584E+18
WichmannHill1982¶
-
dipy.core.rng.
WichmannHill1982
()¶ Algorithm AS 183 Appl. Statist. (1982) vol.31, no.2
Returns a pseudo-random number rectangularly distributed between 0 and 1. The cycle length is 6.95E+12 (See page 123 of Applied Statistics (1984) vol.33), not as claimed in the original article.
ix, iy and iz should be set to integer values between 1 and 30000 before the first entry.
Integer arithmetic up to 5212632 is required.
WichmannHill2006¶
-
dipy.core.rng.
WichmannHill2006
()¶ B.A. Wichmann, I.D. Hill, Generating good pseudo-random numbers, Computational Statistics & Data Analysis, Volume 51, Issue 3, 1 December 2006, Pages 1614-1622, ISSN 0167-9473, DOI: 10.1016/j.csda.2006.05.019. (http://www.sciencedirect.com/science/article/B6V8V-4K7F86W-2/2/a3a33291b8264e4c882a8f21b6e43351) for advice on generating many sequences for use together, and on alternative algorithms and codes
Examples
>>> from dipy.core import rng >>> rng.ix, rng.iy, rng.iz, rng.it = 100001, 200002, 300003, 400004 >>> N = 1000 >>> a = [rng.WichmannHill2006() for i in range(N)]
architecture¶
-
dipy.core.rng.
architecture
(executable='/Users/koudoro/anaconda/envs/dipy_dev_3/bin/python', bits='', linkage='')¶ Queries the given executable (defaults to the Python interpreter binary) for various architecture information.
Returns a tuple (bits, linkage) which contains information about the bit architecture and the linkage format used for the executable. Both values are returned as strings.
Values that cannot be determined are returned as given by the parameter presets. If bits is given as ‘’, the sizeof(pointer) (or sizeof(long) on Python version < 1.5.2) is used as indicator for the supported pointer size.
The function relies on the system’s “file” command to do the actual work. This is available on most if not all Unix platforms. On some non-Unix platforms where the “file” command does not exist and the executable is set to the Python interpreter binary defaults from _default_architecture are used.
floor¶
-
dipy.core.rng.
floor
(x)¶ Return the floor of x as an Integral. This is the largest integer <= x.
HemiSphere
¶
-
class
dipy.core.sphere.
HemiSphere
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None, tol=1e-05)¶ Bases:
dipy.core.sphere.Sphere
Points on the unit sphere.
A HemiSphere is similar to a Sphere but it takes antipodal symmetry into account. Antipodal symmetry means that point v on a HemiSphere is the same as the point -v. Duplicate points are discarded when constructing a HemiSphere (including antipodal duplicates). edges and faces are remapped to the remaining points as closely as possible.
The HemiSphere can be constructed using one of three conventions:
HemiSphere(x, y, z) HemiSphere(xyz=xyz) HemiSphere(theta=theta, phi=phi)
- Parameters
- x, y, z1-D array_like
Vertices as x-y-z coordinates.
- theta, phi1-D array_like
Vertices as spherical coordinates. Theta and phi are the inclination and azimuth angles respectively.
- xyz(N, 3) ndarray
Vertices as x-y-z coordinates.
- faces(N, 3) ndarray
Indices into vertices that form triangular faces. If unspecified, the faces are computed using a Delaunay triangulation.
- edges(N, 2) ndarray
Edges between vertices. If unspecified, the edges are derived from the faces.
- tolfloat
Angle in degrees. Vertices that are less than tol degrees apart are treated as duplicates.
See also
- Attributes
- x
- y
- z
Methods
find_closest
(xyz)Find the index of the vertex in the Sphere closest to the input vector, taking into account antipodal symmetry
from_sphere
(sphere[, tol])Create instance from a Sphere
mirror
()Create a full Sphere from a HemiSphere
subdivide
([n])Create a more subdivided HemiSphere
edges
faces
vertices
-
__init__
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None, tol=1e-05)¶ Create a HemiSphere from points
-
faces
()¶
-
find_closest
(xyz)¶ Find the index of the vertex in the Sphere closest to the input vector, taking into account antipodal symmetry
- Parameters
- xyzarray-like, 3 elements
A unit vector
- Returns
- idxint
The index into the Sphere.vertices array that gives the closest vertex (in angle).
-
classmethod
from_sphere
(sphere, tol=1e-05)¶ Create instance from a Sphere
-
mirror
()¶ Create a full Sphere from a HemiSphere
-
subdivide
(n=1)¶ Create a more subdivided HemiSphere
See Sphere.subdivide for full documentation.
Sphere
¶
-
class
dipy.core.sphere.
Sphere
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None)¶ Bases:
object
Points on the unit sphere.
The sphere can be constructed using one of three conventions:
Sphere(x, y, z) Sphere(xyz=xyz) Sphere(theta=theta, phi=phi)
- Parameters
- x, y, z1-D array_like
Vertices as x-y-z coordinates.
- theta, phi1-D array_like
Vertices as spherical coordinates. Theta and phi are the inclination and azimuth angles respectively.
- xyz(N, 3) ndarray
Vertices as x-y-z coordinates.
- faces(N, 3) ndarray
Indices into vertices that form triangular faces. If unspecified, the faces are computed using a Delaunay triangulation.
- edges(N, 2) ndarray
Edges between vertices. If unspecified, the edges are derived from the faces.
- Attributes
- x
- y
- z
Methods
find_closest
(xyz)Find the index of the vertex in the Sphere closest to the input vector
subdivide
([n])Subdivides each face of the sphere into four new faces.
edges
faces
vertices
-
__init__
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None)¶ Initialize self. See help(type(self)) for accurate signature.
-
edges
()¶
-
faces
()¶
-
find_closest
(xyz)¶ Find the index of the vertex in the Sphere closest to the input vector
- Parameters
- xyzarray-like, 3 elements
A unit vector
- Returns
- idxint
The index into the Sphere.vertices array that gives the closest vertex (in angle).
-
subdivide
(n=1)¶ Subdivides each face of the sphere into four new faces.
New vertices are created at a, b, and c. Then each face [x, y, z] is divided into faces [x, a, c], [y, a, b], [z, b, c], and [a, b, c].
y / / a/____ /\ / / \ / /____\/____ x c z
- Parameters
- nint, optional
The number of subdivisions to preform.
- Returns
- new_sphereSphere
The subdivided sphere.
-
vertices
()¶
-
property
x
¶
-
property
y
¶
-
property
z
¶
auto_attr¶
-
dipy.core.sphere.
auto_attr
(func)¶ Decorator to create OneTimeProperty attributes.
- Parameters
- funcmethod
The method that will be called the first time to compute a value. Afterwards, the method’s name will be a standard attribute holding the value of this computation.
Examples
>>> class MagicProp(object): ... @auto_attr ... def a(self): ... return 99 ... >>> x = MagicProp() >>> 'a' in x.__dict__ False >>> x.a 99 >>> 'a' in x.__dict__ True
cart2sphere¶
-
dipy.core.sphere.
cart2sphere
(x, y, z)¶ Return angles for Cartesian 3D coordinates x, y, and z
See doc for
sphere2cart
for angle conventions and derivation of the formulae.\(0\le\theta\mathrm{(theta)}\le\pi\) and \(-\pi\le\phi\mathrm{(phi)}\le\pi\)
- Parameters
- xarray_like
x coordinate in Cartesian space
- yarray_like
y coordinate in Cartesian space
- zarray_like
z coordinate
- Returns
- rarray
radius
- thetaarray
inclination (polar) angle
- phiarray
azimuth angle
disperse_charges¶
-
dipy.core.sphere.
disperse_charges
(hemi, iters, const=0.2)¶ Models electrostatic repulsion on the unit sphere
Places charges on a sphere and simulates the repulsive forces felt by each one. Allows the charges to move for some number of iterations and returns their final location as well as the total potential of the system at each step.
- Parameters
- hemiHemiSphere
Points on a unit sphere.
- itersint
Number of iterations to run.
- constfloat
Using a smaller const could provide a more accurate result, but will need more iterations to converge.
- Returns
- hemiHemiSphere
Distributed points on a unit sphere.
- potentialndarray
The electrostatic potential at each iteration. This can be useful to check if the repulsion converged to a minimum.
Notes
This function is meant to be used with diffusion imaging so antipodal symmetry is assumed. Therefor each charge must not only be unique, but if there is a charge at +x, there cannot be a charge at -x. These are treated as the same location and because the distance between the two charges will be zero, the result will be unstable.
euler_characteristic_check¶
-
dipy.core.sphere.
euler_characteristic_check
(sphere, chi=2)¶ Checks the euler characteristic of a sphere
If \(f\) = number of faces, \(e\) = number_of_edges and \(v\) = number of vertices, the Euler formula says \(f-e+v = 2\) for a mesh on a sphere. More generally, whether \(f -e + v == \chi\) where \(\chi\) is the Euler characteristic of the mesh.
Open chain (track) has \(\chi=1\)
Closed chain (loop) has \(\chi=0\)
Disk has \(\chi=1\)
Sphere has \(\chi=2\)
HemiSphere has \(\chi=1\)
- Parameters
- sphereSphere
A Sphere instance with vertices, edges and faces attributes.
- chiint, optional
The Euler characteristic of the mesh to be checked
- Returns
- checkbool
True if the mesh has Euler characteristic \(\chi\)
Examples
>>> euler_characteristic_check(unit_octahedron) True >>> hemisphere = HemiSphere.from_sphere(unit_icosahedron) >>> euler_characteristic_check(hemisphere, chi=1) True
faces_from_sphere_vertices¶
-
dipy.core.sphere.
faces_from_sphere_vertices
(vertices)¶ Triangulate a set of vertices on the sphere.
- Parameters
- vertices(M, 3) ndarray
XYZ coordinates of vertices on the sphere.
- Returns
- faces(N, 3) ndarray
Indices into vertices; forms triangular faces.
remove_similar_vertices¶
-
dipy.core.sphere.
remove_similar_vertices
()¶ Remove vertices that are less than theta degrees from any other
Returns vertices that are at least theta degrees from any other vertex. Vertex v and -v are considered the same so if v and -v are both in vertices only one is kept. Also if v and w are both in vertices, w must be separated by theta degrees from both v and -v to be unique.
- Parameters
- vertices(N, 3) ndarray
N unit vectors.
- thetafloat
The minimum separation between vertices in degrees.
- return_mapping{False, True}, optional
If True, return mapping as well as vertices and maybe indices (see below).
- return_indices{False, True}, optional
If True, return indices as well as vertices and maybe mapping (see below).
- Returns
- unique_vertices(M, 3) ndarray
Vertices sufficiently separated from one another.
- mapping(N,) ndarray
For each element
vertices[i]
(\(i \in 0..N-1\)), the index \(j\) to a vertex in unique_vertices that is less than theta degrees fromvertices[i]
. Only returned if return_mapping is True.- indices(N,) ndarray
indices gives the reverse of mapping. For each element
unique_vertices[j]
(\(j \in 0..M-1\)), the index \(i\) to a vertex in vertices that is less than theta degrees fromunique_vertices[j]
. If there is more than one element of vertices that is less than theta degrees from unique_vertices[j], return the first (lowest index) matching value. Only return if return_indices is True.
sphere2cart¶
-
dipy.core.sphere.
sphere2cart
(r, theta, phi)¶ Spherical to Cartesian coordinates
This is the standard physics convention where theta is the inclination (polar) angle, and phi is the azimuth angle.
Imagine a sphere with center (0,0,0). Orient it with the z axis running south-north, the y axis running west-east and the x axis from posterior to anterior. theta (the inclination angle) is the angle to rotate from the z-axis (the zenith) around the y-axis, towards the x axis. Thus the rotation is counter-clockwise from the point of view of positive y. phi (azimuth) gives the angle of rotation around the z-axis towards the y axis. The rotation is counter-clockwise from the point of view of positive z.
Equivalently, given a point P on the sphere, with coordinates x, y, z, theta is the angle between P and the z-axis, and phi is the angle between the projection of P onto the XY plane, and the X axis.
Geographical nomenclature designates theta as ‘co-latitude’, and phi as ‘longitude’
- Parameters
- rarray_like
radius
- thetaarray_like
inclination or polar angle
- phiarray_like
azimuth angle
- Returns
- xarray
x coordinate(s) in Cartesion space
- yarray
y coordinate(s) in Cartesian space
- zarray
z coordinate
Notes
See these pages:
for excellent discussion of the many different conventions possible. Here we use the physics conventions, used in the wikipedia page.
Derivations of the formulae are simple. Consider a vector x, y, z of length r (norm of x, y, z). The inclination angle (theta) can be found from: cos(theta) == z / r -> z == r * cos(theta). This gives the hypotenuse of the projection onto the XY plane, which we will call Q. Q == r*sin(theta). Now x / Q == cos(phi) -> x == r * sin(theta) * cos(phi) and so on.
We have deliberately named this function
sphere2cart
rather thansph2cart
to distinguish it from the Matlab function of that name, because the Matlab function uses an unusual convention for the angles that we did not want to replicate. The Matlab function is trivial to implement with the formulae given in the Matlab help.
unique_edges¶
-
dipy.core.sphere.
unique_edges
(faces, return_mapping=False)¶ Extract all unique edges from given triangular faces.
- Parameters
- faces(N, 3) ndarray
Vertex indices forming triangular faces.
- return_mappingbool
If true, a mapping to the edges of each face is returned.
- Returns
- edges(N, 2) ndarray
Unique edges.
- mapping(N, 3)
For each face, [x, y, z], a mapping to it’s edges [a, b, c].
y / / a/ / / /__________ x c z
unique_sets¶
-
dipy.core.sphere.
unique_sets
(sets, return_inverse=False)¶ Remove duplicate sets.
- Parameters
- setsarray (N, k)
N sets of size k.
- return_inversebool
If True, also returns the indices of unique_sets that can be used to reconstruct sets (the original ordering of each set may not be preserved).
- Returns
- unique_setsarray
Unique sets.
- inversearray (N,)
The indices to reconstruct sets from unique_sets.
vector_norm¶
-
dipy.core.sphere.
vector_norm
(vec, axis=-1, keepdims=False)¶ Return vector Euclidean (L2) norm
See unit vector and Euclidean norm
- Parameters
- vecarray_like
Vectors to norm.
- axisint
Axis over which to norm. By default norm over last axis. If axis is None, vec is flattened then normed.
- keepdimsbool
If True, the output will have the same number of dimensions as vec, with shape 1 on axis.
- Returns
- normarray
Euclidean norms of vectors.
Examples
>>> import numpy as np >>> vec = [[8, 15, 0], [0, 36, 77]] >>> vector_norm(vec) array([ 17., 85.]) >>> vector_norm(vec, keepdims=True) array([[ 17.], [ 85.]]) >>> vector_norm(vec, axis=0) array([ 8., 39., 77.])
permutations
¶
-
class
dipy.core.sphere_stats.
permutations
¶ Bases:
object
permutations(iterable[, r]) –> permutations object
Return successive r-length permutations of elements in the iterable.
permutations(range(3), 2) –> (0,1), (0,2), (1,0), (1,2), (2,0), (2,1)
-
__init__
($self, /, *args, **kwargs)¶ Initialize self. See help(type(self)) for accurate signature.
-
angular_similarity¶
-
dipy.core.sphere_stats.
angular_similarity
(S, T)¶ Computes the cosine distance of the best match between points of two sets of vectors S and T
- Parameters
- Sarray, shape (m,d)
- Tarray, shape (n,d)
- Returns
- max_cosine_distance:float
Examples
>>> import numpy as np >>> from dipy.core.sphere_stats import angular_similarity >>> S=np.array([[1,0,0],[0,1,0],[0,0,1]]) >>> T=np.array([[1,0,0],[0,0,1]]) >>> angular_similarity(S,T) 2.0 >>> T=np.array([[0,1,0],[1,0,0],[0,0,1]]) >>> S=np.array([[1,0,0],[0,0,1]]) >>> angular_similarity(S,T) 2.0 >>> S=np.array([[-1,0,0],[0,1,0],[0,0,1]]) >>> T=np.array([[1,0,0],[0,0,-1]]) >>> angular_similarity(S,T) 2.0 >>> T=np.array([[0,1,0],[1,0,0],[0,0,1]]) >>> S=np.array([[1,0,0],[0,1,0],[0,0,1]]) >>> angular_similarity(S,T) 3.0 >>> S=np.array([[0,1,0],[1,0,0],[0,0,1]]) >>> T=np.array([[1,0,0],[0,np.sqrt(2)/2.,np.sqrt(2)/2.],[0,0,1]]) >>> angular_similarity(S,T) 2.7071067811865475 >>> S=np.array([[0,1,0],[1,0,0],[0,0,1]]) >>> T=np.array([[1,0,0]]) >>> angular_similarity(S,T) 1.0 >>> S=np.array([[0,1,0],[1,0,0]]) >>> T=np.array([[0,0,1]]) >>> angular_similarity(S,T) 0.0 >>> S=np.array([[0,1,0],[1,0,0]]) >>> T=np.array([[0,np.sqrt(2)/2.,np.sqrt(2)/2.]])
Now we use
print
to reduce the precision of of the printed output (so the doctests don’t detect unimportant differences)>>> print('%.12f' % angular_similarity(S,T)) 0.707106781187 >>> S=np.array([[0,1,0]]) >>> T=np.array([[0,np.sqrt(2)/2.,np.sqrt(2)/2.]]) >>> print('%.12f' % angular_similarity(S,T)) 0.707106781187 >>> S=np.array([[0,1,0],[0,0,1]]) >>> T=np.array([[0,np.sqrt(2)/2.,np.sqrt(2)/2.]]) >>> print('%.12f' % angular_similarity(S,T)) 0.707106781187
compare_orientation_sets¶
-
dipy.core.sphere_stats.
compare_orientation_sets
(S, T)¶ Computes the mean cosine distance of the best match between points of two sets of vectors S and T (angular similarity)
- Parameters
- Sarray, shape (m,d)
First set of vectors.
- Tarray, shape (n,d)
Second set of vectors.
- Returns
- max_mean_cosinefloat
Maximum mean cosine distance.
Examples
>>> from dipy.core.sphere_stats import compare_orientation_sets >>> S=np.array([[1,0,0],[0,1,0],[0,0,1]]) >>> T=np.array([[1,0,0],[0,0,1]]) >>> compare_orientation_sets(S,T) 1.0 >>> T=np.array([[0,1,0],[1,0,0],[0,0,1]]) >>> S=np.array([[1,0,0],[0,0,1]]) >>> compare_orientation_sets(S,T) 1.0 >>> from dipy.core.sphere_stats import compare_orientation_sets >>> S=np.array([[-1,0,0],[0,1,0],[0,0,1]]) >>> T=np.array([[1,0,0],[0,0,-1]]) >>> compare_orientation_sets(S,T) 1.0
eigenstats¶
-
dipy.core.sphere_stats.
eigenstats
(points, alpha=0.05)¶ Principal direction and confidence ellipse
Implements equations in section 6.3.1(ii) of Fisher, Lewis and Embleton, supplemented by equations in section 3.2.5.
- Parameters
- pointsarraey_like (N,3)
array of points on the sphere of radius 1 in \(\mathbb{R}^3\)
- alphareal or None
1 minus the coverage for the confidence ellipsoid, e.g. 0.05 for 95% coverage.
- Returns
- centrevector (3,)
centre of ellipsoid
- b1vector (2,)
lengths of semi-axes of ellipsoid
random_uniform_on_sphere¶
-
dipy.core.sphere_stats.
random_uniform_on_sphere
(n=1, coords='xyz')¶ Random unit vectors from a uniform distribution on the sphere.
- Parameters
- nint
Number of random vectors
- coords{‘xyz’, ‘radians’, ‘degrees’}
‘xyz’ for cartesian form ‘radians’ for spherical form in rads ‘degrees’ for spherical form in degrees
- Returns
- Xarray, shape (n,3) if coords=’xyz’ or shape (n,2) otherwise
Uniformly distributed vectors on the unit sphere.
Notes
The uniform distribution on the sphere, parameterized by spherical coordinates \((\theta, \phi)\), should verify \(\phi\sim U[0,2\pi]\), while \(z=\cos(\theta)\sim U[-1,1]\).
References
Examples
>>> from dipy.core.sphere_stats import random_uniform_on_sphere >>> X = random_uniform_on_sphere(4, 'radians') >>> X.shape == (4, 2) True >>> X = random_uniform_on_sphere(4, 'xyz') >>> X.shape == (4, 3) True
HemiSphere
¶
-
class
dipy.core.subdivide_octahedron.
HemiSphere
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None, tol=1e-05)¶ Bases:
dipy.core.sphere.Sphere
Points on the unit sphere.
A HemiSphere is similar to a Sphere but it takes antipodal symmetry into account. Antipodal symmetry means that point v on a HemiSphere is the same as the point -v. Duplicate points are discarded when constructing a HemiSphere (including antipodal duplicates). edges and faces are remapped to the remaining points as closely as possible.
The HemiSphere can be constructed using one of three conventions:
HemiSphere(x, y, z) HemiSphere(xyz=xyz) HemiSphere(theta=theta, phi=phi)
- Parameters
- x, y, z1-D array_like
Vertices as x-y-z coordinates.
- theta, phi1-D array_like
Vertices as spherical coordinates. Theta and phi are the inclination and azimuth angles respectively.
- xyz(N, 3) ndarray
Vertices as x-y-z coordinates.
- faces(N, 3) ndarray
Indices into vertices that form triangular faces. If unspecified, the faces are computed using a Delaunay triangulation.
- edges(N, 2) ndarray
Edges between vertices. If unspecified, the edges are derived from the faces.
- tolfloat
Angle in degrees. Vertices that are less than tol degrees apart are treated as duplicates.
See also
Sphere
- Attributes
- x
- y
- z
Methods
find_closest
(xyz)Find the index of the vertex in the Sphere closest to the input vector, taking into account antipodal symmetry
from_sphere
(sphere[, tol])Create instance from a Sphere
mirror
()Create a full Sphere from a HemiSphere
subdivide
([n])Create a more subdivided HemiSphere
edges
faces
vertices
-
__init__
(x=None, y=None, z=None, theta=None, phi=None, xyz=None, faces=None, edges=None, tol=1e-05)¶ Create a HemiSphere from points
-
faces
()¶
-
find_closest
(xyz)¶ Find the index of the vertex in the Sphere closest to the input vector, taking into account antipodal symmetry
- Parameters
- xyzarray-like, 3 elements
A unit vector
- Returns
- idxint
The index into the Sphere.vertices array that gives the closest vertex (in angle).
-
classmethod
from_sphere
(sphere, tol=1e-05)¶ Create instance from a Sphere
-
mirror
()¶ Create a full Sphere from a HemiSphere
-
subdivide
(n=1)¶ Create a more subdivided HemiSphere
See Sphere.subdivide for full documentation.
create_unit_hemisphere¶
-
dipy.core.subdivide_octahedron.
create_unit_hemisphere
(recursion_level=2)¶ Creates a unit sphere by subdividing a unit octahedron, returns half the sphere.
- Parameters
- recursion_levelint
Level of subdivision, recursion_level=1 will return an octahedron, anything bigger will return a more subdivided sphere. The sphere will have \((4^recursion_level+2)/2\) vertices.
- Returns
- HemiSphere :
Half of a unit sphere.
See also
create_unit_sphere
,Sphere
,HemiSphere
create_unit_sphere¶
-
dipy.core.subdivide_octahedron.
create_unit_sphere
(recursion_level=2)¶ Creates a unit sphere by subdividing a unit octahedron.
Starts with a unit octahedron and subdivides the faces, projecting the resulting points onto the surface of a unit sphere.
- Parameters
- recursion_levelint
Level of subdivision, recursion_level=1 will return an octahedron, anything bigger will return a more subdivided sphere. The sphere will have \(4^recursion_level+2\) vertices.
- Returns
- Sphere :
The unit sphere.
See also
create_unit_hemisphere
,Sphere
afb3D¶
-
dipy.core.wavelet.
afb3D
(x, af1, af2=None, af3=None)¶ 3D Analysis Filter Bank
- Parameters
- x3D ndarray
N1 by N2 by N3 array matrix, where 1) N1, N2, N3 all even 2) N1 >= 2*len(af1) 3) N2 >= 2*len(af2) 4) N3 >= 2*len(af3)
- afi2D ndarray
analysis filters for dimension i afi[:, 1] - lowpass filter afi[:, 2] - highpass filter
- Returns
- lo1D array
lowpass subband
- hi1D array
highpass subbands, h[d]- d = 1..7
afb3D_A¶
-
dipy.core.wavelet.
afb3D_A
(x, af, d)¶ - 3D Analysis Filter Bank
(along one dimension only)
- Parameters
- x3D ndarray
- N1xN2xN2 matrix, where min(N1,N2,N3) > 2*length(filter)
(Ni are even)
- af2D ndarray
analysis filter for the columns af[:, 1] - lowpass filter af[:, 2] - highpass filter
- dint
dimension of filtering (d = 1, 2 or 3)
- Returns
- lo1D array
lowpass subbands
- hi1D array
highpass subbands
cshift3D¶
-
dipy.core.wavelet.
cshift3D
(x, m, d)¶ 3D Circular Shift
- Parameters
- x3D ndarray
N1 by N2 by N3 array
- mint
amount of shift
- dint
dimension of shift (d = 1,2,3)
- Returns
- y3D ndarray
array x will be shifed by m samples down along dimension d
dwt3D¶
-
dipy.core.wavelet.
dwt3D
(x, J, af)¶ 3-D Discrete Wavelet Transform
- Parameters
- x3D ndarray
N1 x N2 x N3 matrix 1) Ni all even 2) min(Ni) >= 2^(J-1)*length(af)
- Jint
number of stages
- af2D ndarray
analysis filters
- Returns
- wcell array
wavelet coefficients
idwt3D¶
-
dipy.core.wavelet.
idwt3D
(w, J, sf)¶ Inverse 3-D Discrete Wavelet Transform
- Parameters
- wcell array
wavelet coefficient
- Jint
number of stages
- sf2D ndarray
synthesis filters
- Returns
- y3D ndarray
output array
permutationinverse¶
-
dipy.core.wavelet.
permutationinverse
(perm)¶ Function generating inverse of the permutation
- Parameters
- perm1D array
- Returns
- inverse1D array
permutation inverse of the input