Source code for dipy.core.rng
"""Random number generation utilities."""
from math import floor
from platform import architecture
import numpy as np
from dipy.testing.decorators import warning_for_keywords
[docs]
@warning_for_keywords()
def WichmannHill2006(*, ix=100001, iy=200002, iz=300003, it=400004):
"""Wichmann Hill random number generator.
See :footcite:p:`Wichmann2006` for advice on generating many sequences for
use together, and on alternative algorithms and codes
Parameters
----------
ix: int
First seed value. Should not be null. (default 100001)
iy: int
Second seed value. Should not be null. (default 200002)
iz: int
Third seed value. Should not be null. (default 300003)
it: int
Fourth seed value. Should not be null. (default 400004)
Returns
-------
r_number : float
pseudo-random number uniformly distributed between [0-1]
References
----------
.. footbibliography::
Examples
--------
>>> from dipy.core import rng
>>> N = 1000
>>> a = [rng.WichmannHill2006() for i in range(N)]
"""
if not ix or not iy or not iz or not it:
raise ValueError("A seed value can not be null.")
if architecture()[0] == "64":
# If 64 bits are available then the following lines of code will be
# faster.
ix = (11600 * ix) % 2147483579
iy = (47003 * iy) % 2147483543
iz = (23000 * iz) % 2147483423
it = (33000 * it) % 2147483123
else:
# If only 32 bits are available
ix = 11600 * (ix % 185127) - 10379 * (ix / 185127)
iy = 47003 * (ix % 45688) - 10479 * (iy / 45688)
iz = 23000 * (iz % 93368) - 19423 * (iz / 93368)
it = 33000 * (it % 65075) - 8123 * (it / 65075)
if ix < 0:
ix = ix + 2147483579
if iy < 0:
iy = iy + 2147483543
if iz < 0:
iz = iz + 2147483423
if it < 0:
it = it + 2147483123
W = ix / 2147483579.0 + iy / 2147483543.0 + iz / 2147483423.0 + it / 2147483123.0
return W - floor(W)
[docs]
@warning_for_keywords()
def WichmannHill1982(*, ix=100001, iy=200002, iz=300003):
"""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.
Parameters
----------
ix: int
First seed value. Should not be null. (default 100001)
iy: int
Second seed value. Should not be null. (default 200002)
iz: int
Third seed value. Should not be null. (default 300003)
Returns
-------
r_number : float
pseudo-random number uniformly distributed between [0-1]
Examples
--------
>>> from dipy.core import rng
>>> N = 1000
>>> a = [rng.WichmannHill1982() for i in range(N)]
"""
if not ix or not iy or not iz:
raise ValueError("A seed value can not be null.")
ix = (171 * ix) % 30269
iy = (172 * iy) % 30307
iz = (170 * iz) % 30323
"""
If integer arithmetic only up to 30323 (!) is available, the preceding
3 statements may be replaced by:
ix = 171 * (ix % 177) - 2 * (ix / 177)
iy = 172 * (iy % 176) - 35 * (iy / 176)
iz = 170 * (iz % 178) - 63 * (iz / 178)
if ix < 0:
ix = ix + 30269
if iy < 0:
iy = iy + 30307
if iz < 0:
iz = iz + 30323
"""
return np.remainder(
float(ix) / 30269.0 + float(iy) / 30307.0 + float(iz) / 30323.0, 1.0
)
[docs]
@warning_for_keywords()
def LEcuyer(*, s1=100001, s2=200002):
"""Return a LEcuyer random number generator.
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
Parameters
----------
s1: int
First seed value. Should not be null. (default 100001)
s2: int
Second seed value. Should not be null. (default 200002)
Returns
-------
r_number : float
pseudo-random number uniformly distributed between [0-1]
Examples
--------
>>> from dipy.core import rng
>>> N = 1000
>>> a = [rng.LEcuyer() for i in range(N)]
"""
if not s1 or not s2:
raise ValueError("A seed value can not be null.")
k = s1 / 53668
s1 = 40014 * (s1 - k * 53668) - k * 12211
if s1 < 0:
s1 = s1 + 2147483563
k = s2 / 52774
s2 = 40692 * (s2 - k * 52774) - k * 3791
if s2 < 0:
s2 = s2 + 2147483399
z = s1 - s2
if z < 0:
z = z + 2147483562
return z / 2147483563.0