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/ special / basic.py
#
# Author: Travis Oliphant, 2002
#
from __future__ import division, print_function, absolute_import
import operator
import numpy as np
import math
from scipy._lib.six import xrange
from numpy import (pi, asarray, floor, isscalar, iscomplex, real,
imag, sqrt, where, mgrid, sin, place, issubdtype,
extract, inexact, nan, zeros, sinc)
from . import _ufuncs as ufuncs
from ._ufuncs import (ellipkm1, mathieu_a, mathieu_b, iv, jv, gamma,
psi, _zeta, hankel1, hankel2, yv, kv, ndtri,
poch, binom, hyp0f1)
from . import specfun
from . import orthogonal
from ._comb import _comb_int
__all__ = ['ai_zeros', 'assoc_laguerre', 'bei_zeros', 'beip_zeros',
'ber_zeros', 'bernoulli', 'berp_zeros',
'bessel_diff_formula', 'bi_zeros', 'clpmn', 'comb',
'digamma', 'diric', 'ellipk', 'erf_zeros', 'erfcinv',
'erfinv', 'euler', 'factorial', 'factorialk', 'factorial2',
'fresnel_zeros', 'fresnelc_zeros', 'fresnels_zeros',
'gamma', 'h1vp', 'h2vp', 'hankel1', 'hankel2', 'hyp0f1',
'iv', 'ivp', 'jn_zeros', 'jnjnp_zeros', 'jnp_zeros',
'jnyn_zeros', 'jv', 'jvp', 'kei_zeros', 'keip_zeros',
'kelvin_zeros', 'ker_zeros', 'kerp_zeros', 'kv', 'kvp',
'lmbda', 'lpmn', 'lpn', 'lqmn', 'lqn', 'mathieu_a',
'mathieu_b', 'mathieu_even_coef', 'mathieu_odd_coef',
'ndtri', 'obl_cv_seq', 'pbdn_seq', 'pbdv_seq', 'pbvv_seq',
'perm', 'polygamma', 'pro_cv_seq', 'psi', 'riccati_jn',
'riccati_yn', 'sinc', 'y0_zeros', 'y1_zeros', 'y1p_zeros',
'yn_zeros', 'ynp_zeros', 'yv', 'yvp', 'zeta']
def _nonneg_int_or_fail(n, var_name, strict=True):
try:
if strict:
# Raises an exception if float
n = operator.index(n)
elif n == floor(n):
n = int(n)
else:
raise ValueError()
if n < 0:
raise ValueError()
except (ValueError, TypeError) as err:
raise err.__class__("{} must be a non-negative integer".format(var_name))
return n
def diric(x, n):
"""Periodic sinc function, also called the Dirichlet function.
The Dirichlet function is defined as::
diric(x, n) = sin(x * n/2) / (n * sin(x / 2)),
where `n` is a positive integer.
Parameters
----------
x : array_like
Input data
n : int
Integer defining the periodicity.
Returns
-------
diric : ndarray
Examples
--------
>>> from scipy import special
>>> import matplotlib.pyplot as plt
>>> x = np.linspace(-8*np.pi, 8*np.pi, num=201)
>>> plt.figure(figsize=(8, 8));
>>> for idx, n in enumerate([2, 3, 4, 9]):
... plt.subplot(2, 2, idx+1)
... plt.plot(x, special.diric(x, n))
... plt.title('diric, n={}'.format(n))
>>> plt.show()
The following example demonstrates that `diric` gives the magnitudes
(modulo the sign and scaling) of the Fourier coefficients of a
rectangular pulse.
Suppress output of values that are effectively 0:
>>> np.set_printoptions(suppress=True)
Create a signal `x` of length `m` with `k` ones:
>>> m = 8
>>> k = 3
>>> x = np.zeros(m)
>>> x[:k] = 1
Use the FFT to compute the Fourier transform of `x`, and
inspect the magnitudes of the coefficients:
>>> np.abs(np.fft.fft(x))
array([ 3. , 2.41421356, 1. , 0.41421356, 1. ,
0.41421356, 1. , 2.41421356])
Now find the same values (up to sign) using `diric`. We multiply
by `k` to account for the different scaling conventions of
`numpy.fft.fft` and `diric`:
>>> theta = np.linspace(0, 2*np.pi, m, endpoint=False)
>>> k * special.diric(theta, k)
array([ 3. , 2.41421356, 1. , -0.41421356, -1. ,
-0.41421356, 1. , 2.41421356])
"""
x, n = asarray(x), asarray(n)
n = asarray(n + (x-x))
x = asarray(x + (n-n))
if issubdtype(x.dtype, inexact):
ytype = x.dtype
else:
ytype = float
y = zeros(x.shape, ytype)
# empirical minval for 32, 64 or 128 bit float computations
# where sin(x/2) < minval, result is fixed at +1 or -1
if np.finfo(ytype).eps < 1e-18:
minval = 1e-11
elif np.finfo(ytype).eps < 1e-15:
minval = 1e-7
else:
minval = 1e-3
mask1 = (n <= 0) | (n != floor(n))
place(y, mask1, nan)
x = x / 2
denom = sin(x)
mask2 = (1-mask1) & (abs(denom) < minval)
xsub = extract(mask2, x)
nsub = extract(mask2, n)
zsub = xsub / pi
place(y, mask2, pow(-1, np.round(zsub)*(nsub-1)))
mask = (1-mask1) & (1-mask2)
xsub = extract(mask, x)
nsub = extract(mask, n)
dsub = extract(mask, denom)
place(y, mask, sin(nsub*xsub)/(nsub*dsub))
return y
def jnjnp_zeros(nt):
"""Compute zeros of integer-order Bessel functions Jn and Jn'.
Results are arranged in order of the magnitudes of the zeros.
Parameters
----------
nt : int
Number (<=1200) of zeros to compute
Returns
-------
zo[l-1] : ndarray
Value of the lth zero of Jn(x) and Jn'(x). Of length `nt`.
n[l-1] : ndarray
Order of the Jn(x) or Jn'(x) associated with lth zero. Of length `nt`.
m[l-1] : ndarray
Serial number of the zeros of Jn(x) or Jn'(x) associated
with lth zero. Of length `nt`.
t[l-1] : ndarray
0 if lth zero in zo is zero of Jn(x), 1 if it is a zero of Jn'(x). Of
length `nt`.
See Also
--------
jn_zeros, jnp_zeros : to get separated arrays of zeros.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt > 1200):
raise ValueError("Number must be integer <= 1200.")
nt = int(nt)
n, m, t, zo = specfun.jdzo(nt)
return zo[1:nt+1], n[:nt], m[:nt], t[:nt]
def jnyn_zeros(n, nt):
"""Compute nt zeros of Bessel functions Jn(x), Jn'(x), Yn(x), and Yn'(x).
Returns 4 arrays of length `nt`, corresponding to the first `nt` zeros of
Jn(x), Jn'(x), Yn(x), and Yn'(x), respectively.
Parameters
----------
n : int
Order of the Bessel functions
nt : int
Number (<=1200) of zeros to compute
See jn_zeros, jnp_zeros, yn_zeros, ynp_zeros to get separate arrays.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(nt) and isscalar(n)):
raise ValueError("Arguments must be scalars.")
if (floor(n) != n) or (floor(nt) != nt):
raise ValueError("Arguments must be integers.")
if (nt <= 0):
raise ValueError("nt > 0")
return specfun.jyzo(abs(n), nt)
def jn_zeros(n, nt):
"""Compute zeros of integer-order Bessel function Jn(x).
Parameters
----------
n : int
Order of Bessel function
nt : int
Number of zeros to return
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
return jnyn_zeros(n, nt)[0]
def jnp_zeros(n, nt):
"""Compute zeros of integer-order Bessel function derivative Jn'(x).
Parameters
----------
n : int
Order of Bessel function
nt : int
Number of zeros to return
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
return jnyn_zeros(n, nt)[1]
def yn_zeros(n, nt):
"""Compute zeros of integer-order Bessel function Yn(x).
Parameters
----------
n : int
Order of Bessel function
nt : int
Number of zeros to return
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
return jnyn_zeros(n, nt)[2]
def ynp_zeros(n, nt):
"""Compute zeros of integer-order Bessel function derivative Yn'(x).
Parameters
----------
n : int
Order of Bessel function
nt : int
Number of zeros to return
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
return jnyn_zeros(n, nt)[3]
def y0_zeros(nt, complex=False):
"""Compute nt zeros of Bessel function Y0(z), and derivative at each zero.
The derivatives are given by Y0'(z0) = -Y1(z0) at each zero z0.
Parameters
----------
nt : int
Number of zeros to return
complex : bool, default False
Set to False to return only the real zeros; set to True to return only
the complex zeros with negative real part and positive imaginary part.
Note that the complex conjugates of the latter are also zeros of the
function, but are not returned by this routine.
Returns
-------
z0n : ndarray
Location of nth zero of Y0(z)
y0pz0n : ndarray
Value of derivative Y0'(z0) for nth zero
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("Arguments must be scalar positive integer.")
kf = 0
kc = not complex
return specfun.cyzo(nt, kf, kc)
def y1_zeros(nt, complex=False):
"""Compute nt zeros of Bessel function Y1(z), and derivative at each zero.
The derivatives are given by Y1'(z1) = Y0(z1) at each zero z1.
Parameters
----------
nt : int
Number of zeros to return
complex : bool, default False
Set to False to return only the real zeros; set to True to return only
the complex zeros with negative real part and positive imaginary part.
Note that the complex conjugates of the latter are also zeros of the
function, but are not returned by this routine.
Returns
-------
z1n : ndarray
Location of nth zero of Y1(z)
y1pz1n : ndarray
Value of derivative Y1'(z1) for nth zero
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("Arguments must be scalar positive integer.")
kf = 1
kc = not complex
return specfun.cyzo(nt, kf, kc)
def y1p_zeros(nt, complex=False):
"""Compute nt zeros of Bessel derivative Y1'(z), and value at each zero.
The values are given by Y1(z1) at each z1 where Y1'(z1)=0.
Parameters
----------
nt : int
Number of zeros to return
complex : bool, default False
Set to False to return only the real zeros; set to True to return only
the complex zeros with negative real part and positive imaginary part.
Note that the complex conjugates of the latter are also zeros of the
function, but are not returned by this routine.
Returns
-------
z1pn : ndarray
Location of nth zero of Y1'(z)
y1z1pn : ndarray
Value of derivative Y1(z1) for nth zero
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("Arguments must be scalar positive integer.")
kf = 2
kc = not complex
return specfun.cyzo(nt, kf, kc)
def _bessel_diff_formula(v, z, n, L, phase):
# from AMS55.
# L(v, z) = J(v, z), Y(v, z), H1(v, z), H2(v, z), phase = -1
# L(v, z) = I(v, z) or exp(v*pi*i)K(v, z), phase = 1
# For K, you can pull out the exp((v-k)*pi*i) into the caller
v = asarray(v)
p = 1.0
s = L(v-n, z)
for i in xrange(1, n+1):
p = phase * (p * (n-i+1)) / i # = choose(k, i)
s += p*L(v-n + i*2, z)
return s / (2.**n)
bessel_diff_formula = np.deprecate(_bessel_diff_formula,
message="bessel_diff_formula is a private function, do not use it!")
def jvp(v, z, n=1):
"""Compute nth derivative of Bessel function Jv(z) with respect to `z`.
Parameters
----------
v : float
Order of Bessel function
z : complex
Argument at which to evaluate the derivative
n : int, default 1
Order of derivative
Notes
-----
The derivative is computed using the relation DLFM 10.6.7 [2]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.6.E7
"""
n = _nonneg_int_or_fail(n, 'n')
if n == 0:
return jv(v, z)
else:
return _bessel_diff_formula(v, z, n, jv, -1)
def yvp(v, z, n=1):
"""Compute nth derivative of Bessel function Yv(z) with respect to `z`.
Parameters
----------
v : float
Order of Bessel function
z : complex
Argument at which to evaluate the derivative
n : int, default 1
Order of derivative
Notes
-----
The derivative is computed using the relation DLFM 10.6.7 [2]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.6.E7
"""
n = _nonneg_int_or_fail(n, 'n')
if n == 0:
return yv(v, z)
else:
return _bessel_diff_formula(v, z, n, yv, -1)
def kvp(v, z, n=1):
"""Compute nth derivative of real-order modified Bessel function Kv(z)
Kv(z) is the modified Bessel function of the second kind.
Derivative is calculated with respect to `z`.
Parameters
----------
v : array_like of float
Order of Bessel function
z : array_like of complex
Argument at which to evaluate the derivative
n : int
Order of derivative. Default is first derivative.
Returns
-------
out : ndarray
The results
Examples
--------
Calculate multiple values at order 5:
>>> from scipy.special import kvp
>>> kvp(5, (1, 2, 3+5j))
array([-1.84903536e+03+0.j , -2.57735387e+01+0.j ,
-3.06627741e-02+0.08750845j])
Calculate for a single value at multiple orders:
>>> kvp((4, 4.5, 5), 1)
array([ -184.0309, -568.9585, -1849.0354])
Notes
-----
The derivative is computed using the relation DLFM 10.29.5 [2]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 6.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.29.E5
"""
n = _nonneg_int_or_fail(n, 'n')
if n == 0:
return kv(v, z)
else:
return (-1)**n * _bessel_diff_formula(v, z, n, kv, 1)
def ivp(v, z, n=1):
"""Compute nth derivative of modified Bessel function Iv(z) with respect
to `z`.
Parameters
----------
v : array_like of float
Order of Bessel function
z : array_like of complex
Argument at which to evaluate the derivative
n : int, default 1
Order of derivative
Notes
-----
The derivative is computed using the relation DLFM 10.29.5 [2]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 6.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.29.E5
"""
n = _nonneg_int_or_fail(n, 'n')
if n == 0:
return iv(v, z)
else:
return _bessel_diff_formula(v, z, n, iv, 1)
def h1vp(v, z, n=1):
"""Compute nth derivative of Hankel function H1v(z) with respect to `z`.
Parameters
----------
v : float
Order of Hankel function
z : complex
Argument at which to evaluate the derivative
n : int, default 1
Order of derivative
Notes
-----
The derivative is computed using the relation DLFM 10.6.7 [2]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.6.E7
"""
n = _nonneg_int_or_fail(n, 'n')
if n == 0:
return hankel1(v, z)
else:
return _bessel_diff_formula(v, z, n, hankel1, -1)
def h2vp(v, z, n=1):
"""Compute nth derivative of Hankel function H2v(z) with respect to `z`.
Parameters
----------
v : float
Order of Hankel function
z : complex
Argument at which to evaluate the derivative
n : int, default 1
Order of derivative
Notes
-----
The derivative is computed using the relation DLFM 10.6.7 [2]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 5.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.6.E7
"""
n = _nonneg_int_or_fail(n, 'n')
if n == 0:
return hankel2(v, z)
else:
return _bessel_diff_formula(v, z, n, hankel2, -1)
def riccati_jn(n, x):
r"""Compute Ricatti-Bessel function of the first kind and its derivative.
The Ricatti-Bessel function of the first kind is defined as :math:`x
j_n(x)`, where :math:`j_n` is the spherical Bessel function of the first
kind of order :math:`n`.
This function computes the value and first derivative of the
Ricatti-Bessel function for all orders up to and including `n`.
Parameters
----------
n : int
Maximum order of function to compute
x : float
Argument at which to evaluate
Returns
-------
jn : ndarray
Value of j0(x), ..., jn(x)
jnp : ndarray
First derivative j0'(x), ..., jn'(x)
Notes
-----
The computation is carried out via backward recurrence, using the
relation DLMF 10.51.1 [2]_.
Wrapper for a Fortran routine created by Shanjie Zhang and Jianming
Jin [1]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.51.E1
"""
if not (isscalar(n) and isscalar(x)):
raise ValueError("arguments must be scalars.")
n = _nonneg_int_or_fail(n, 'n', strict=False)
if (n == 0):
n1 = 1
else:
n1 = n
nm, jn, jnp = specfun.rctj(n1, x)
return jn[:(n+1)], jnp[:(n+1)]
def riccati_yn(n, x):
"""Compute Ricatti-Bessel function of the second kind and its derivative.
The Ricatti-Bessel function of the second kind is defined as :math:`x
y_n(x)`, where :math:`y_n` is the spherical Bessel function of the second
kind of order :math:`n`.
This function computes the value and first derivative of the function for
all orders up to and including `n`.
Parameters
----------
n : int
Maximum order of function to compute
x : float
Argument at which to evaluate
Returns
-------
yn : ndarray
Value of y0(x), ..., yn(x)
ynp : ndarray
First derivative y0'(x), ..., yn'(x)
Notes
-----
The computation is carried out via ascending recurrence, using the
relation DLMF 10.51.1 [2]_.
Wrapper for a Fortran routine created by Shanjie Zhang and Jianming
Jin [1]_.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions.
https://dlmf.nist.gov/10.51.E1
"""
if not (isscalar(n) and isscalar(x)):
raise ValueError("arguments must be scalars.")
n = _nonneg_int_or_fail(n, 'n', strict=False)
if (n == 0):
n1 = 1
else:
n1 = n
nm, jn, jnp = specfun.rcty(n1, x)
return jn[:(n+1)], jnp[:(n+1)]
def erfinv(y):
"""Inverse of the error function erf.
Computes the inverse of the error function.
In complex domain, there is no unique complex number w satisfying erf(w)=z.
This indicates a true inverse function would have multi-value. When the domain restricts to the real, -1 < x < 1,
there is a unique real number satisfying erf(erfinv(x)) = x.
Parameters
----------
y : ndarray
Argument at which to evaluate. Domain: [-1, 1]
Returns
-------
erfinv : ndarray
The inverse of erf of y, element-wise
Examples
--------
1) evaluating a float number
>>> from scipy import special
>>> special.erfinv(0.5)
0.4769362762044698
2) evaluating a ndarray
>>> from scipy import special
>>> y = np.linspace(-1.0, 1.0, num=10)
>>> special.erfinv(y)
array([ -inf, -0.86312307, -0.5407314 , -0.30457019, -0.0987901 ,
0.0987901 , 0.30457019, 0.5407314 , 0.86312307, inf])
"""
return ndtri((y+1)/2.0)/sqrt(2)
def erfcinv(y):
"""Inverse of the complementary error function erfc.
Computes the inverse of the complementary error function erfc.
In complex domain, there is no unique complex number w satisfying erfc(w)=z.
This indicates a true inverse function would have multi-value. When the domain restricts to the real, 0 < x < 2,
there is a unique real number satisfying erfc(erfcinv(x)) = erfcinv(erfc(x)).
It is related to inverse of the error function by erfcinv(1-x) = erfinv(x)
Parameters
----------
y : ndarray
Argument at which to evaluate. Domain: [0, 2]
Returns
-------
erfcinv : ndarray
The inverse of erfc of y, element-wise
Examples
--------
1) evaluating a float number
>>> from scipy import special
>>> special.erfcinv(0.5)
0.4769362762044698
2) evaluating a ndarray
>>> from scipy import special
>>> y = np.linspace(0.0, 2.0, num=11)
>>> special.erfcinv(y)
array([ inf, 0.9061938 , 0.59511608, 0.37080716, 0.17914345,
-0. , -0.17914345, -0.37080716, -0.59511608, -0.9061938 ,
-inf])
"""
return -ndtri(0.5*y)/sqrt(2)
def erf_zeros(nt):
"""Compute the first nt zero in the first quadrant, ordered by absolute value.
Zeros in the other quadrants can be obtained by using the symmetries erf(-z) = erf(z) and
erf(conj(z)) = conj(erf(z)).
Parameters
----------
nt : int
The number of zeros to compute
Returns
-------
The locations of the zeros of erf : ndarray (complex)
Complex values at which zeros of erf(z)
Examples
--------
>>> from scipy import special
>>> special.erf_zeros(1)
array([1.45061616+1.880943j])
Check that erf is (close to) zero for the value returned by erf_zeros
>>> special.erf(special.erf_zeros(1))
array([4.95159469e-14-1.16407394e-16j])
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if (floor(nt) != nt) or (nt <= 0) or not isscalar(nt):
raise ValueError("Argument must be positive scalar integer.")
return specfun.cerzo(nt)
def fresnelc_zeros(nt):
"""Compute nt complex zeros of cosine Fresnel integral C(z).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if (floor(nt) != nt) or (nt <= 0) or not isscalar(nt):
raise ValueError("Argument must be positive scalar integer.")
return specfun.fcszo(1, nt)
def fresnels_zeros(nt):
"""Compute nt complex zeros of sine Fresnel integral S(z).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if (floor(nt) != nt) or (nt <= 0) or not isscalar(nt):
raise ValueError("Argument must be positive scalar integer.")
return specfun.fcszo(2, nt)
def fresnel_zeros(nt):
"""Compute nt complex zeros of sine and cosine Fresnel integrals S(z) and C(z).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if (floor(nt) != nt) or (nt <= 0) or not isscalar(nt):
raise ValueError("Argument must be positive scalar integer.")
return specfun.fcszo(2, nt), specfun.fcszo(1, nt)
def assoc_laguerre(x, n, k=0.0):
"""Compute the generalized (associated) Laguerre polynomial of degree n and order k.
The polynomial :math:`L^{(k)}_n(x)` is orthogonal over ``[0, inf)``,
with weighting function ``exp(-x) * x**k`` with ``k > -1``.
Notes
-----
`assoc_laguerre` is a simple wrapper around `eval_genlaguerre`, with
reversed argument order ``(x, n, k=0.0) --> (n, k, x)``.
"""
return orthogonal.eval_genlaguerre(n, k, x)
digamma = psi
def polygamma(n, x):
"""Polygamma function n.
This is the nth derivative of the digamma (psi) function.
Parameters
----------
n : array_like of int
The order of the derivative of `psi`.
x : array_like
Where to evaluate the polygamma function.
Returns
-------
polygamma : ndarray
The result.
Examples
--------
>>> from scipy import special
>>> x = [2, 3, 25.5]
>>> special.polygamma(1, x)
array([ 0.64493407, 0.39493407, 0.03999467])
>>> special.polygamma(0, x) == special.psi(x)
array([ True, True, True], dtype=bool)
"""
n, x = asarray(n), asarray(x)
fac2 = (-1.0)**(n+1) * gamma(n+1.0) * zeta(n+1, x)
return where(n == 0, psi(x), fac2)
def mathieu_even_coef(m, q):
r"""Fourier coefficients for even Mathieu and modified Mathieu functions.
The Fourier series of the even solutions of the Mathieu differential
equation are of the form
.. math:: \mathrm{ce}_{2n}(z, q) = \sum_{k=0}^{\infty} A_{(2n)}^{(2k)} \cos 2kz
.. math:: \mathrm{ce}_{2n+1}(z, q) = \sum_{k=0}^{\infty} A_{(2n+1)}^{(2k+1)} \cos (2k+1)z
This function returns the coefficients :math:`A_{(2n)}^{(2k)}` for even
input m=2n, and the coefficients :math:`A_{(2n+1)}^{(2k+1)}` for odd input
m=2n+1.
Parameters
----------
m : int
Order of Mathieu functions. Must be non-negative.
q : float (>=0)
Parameter of Mathieu functions. Must be non-negative.
Returns
-------
Ak : ndarray
Even or odd Fourier coefficients, corresponding to even or odd m.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions
https://dlmf.nist.gov/28.4#i
"""
if not (isscalar(m) and isscalar(q)):
raise ValueError("m and q must be scalars.")
if (q < 0):
raise ValueError("q >=0")
if (m != floor(m)) or (m < 0):
raise ValueError("m must be an integer >=0.")
if (q <= 1):
qm = 7.5 + 56.1*sqrt(q) - 134.7*q + 90.7*sqrt(q)*q
else:
qm = 17.0 + 3.1*sqrt(q) - .126*q + .0037*sqrt(q)*q
km = int(qm + 0.5*m)
if km > 251:
print("Warning, too many predicted coefficients.")
kd = 1
m = int(floor(m))
if m % 2:
kd = 2
a = mathieu_a(m, q)
fc = specfun.fcoef(kd, m, q, a)
return fc[:km]
def mathieu_odd_coef(m, q):
r"""Fourier coefficients for even Mathieu and modified Mathieu functions.
The Fourier series of the odd solutions of the Mathieu differential
equation are of the form
.. math:: \mathrm{se}_{2n+1}(z, q) = \sum_{k=0}^{\infty} B_{(2n+1)}^{(2k+1)} \sin (2k+1)z
.. math:: \mathrm{se}_{2n+2}(z, q) = \sum_{k=0}^{\infty} B_{(2n+2)}^{(2k+2)} \sin (2k+2)z
This function returns the coefficients :math:`B_{(2n+2)}^{(2k+2)}` for even
input m=2n+2, and the coefficients :math:`B_{(2n+1)}^{(2k+1)}` for odd
input m=2n+1.
Parameters
----------
m : int
Order of Mathieu functions. Must be non-negative.
q : float (>=0)
Parameter of Mathieu functions. Must be non-negative.
Returns
-------
Bk : ndarray
Even or odd Fourier coefficients, corresponding to even or odd m.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(m) and isscalar(q)):
raise ValueError("m and q must be scalars.")
if (q < 0):
raise ValueError("q >=0")
if (m != floor(m)) or (m <= 0):
raise ValueError("m must be an integer > 0")
if (q <= 1):
qm = 7.5 + 56.1*sqrt(q) - 134.7*q + 90.7*sqrt(q)*q
else:
qm = 17.0 + 3.1*sqrt(q) - .126*q + .0037*sqrt(q)*q
km = int(qm + 0.5*m)
if km > 251:
print("Warning, too many predicted coefficients.")
kd = 4
m = int(floor(m))
if m % 2:
kd = 3
b = mathieu_b(m, q)
fc = specfun.fcoef(kd, m, q, b)
return fc[:km]
def lpmn(m, n, z):
"""Sequence of associated Legendre functions of the first kind.
Computes the associated Legendre function of the first kind of order m and
degree n, ``Pmn(z)`` = :math:`P_n^m(z)`, and its derivative, ``Pmn'(z)``.
Returns two arrays of size ``(m+1, n+1)`` containing ``Pmn(z)`` and
``Pmn'(z)`` for all orders from ``0..m`` and degrees from ``0..n``.
This function takes a real argument ``z``. For complex arguments ``z``
use clpmn instead.
Parameters
----------
m : int
``|m| <= n``; the order of the Legendre function.
n : int
where ``n >= 0``; the degree of the Legendre function. Often
called ``l`` (lower case L) in descriptions of the associated
Legendre function
z : float
Input value.
Returns
-------
Pmn_z : (m+1, n+1) array
Values for all orders 0..m and degrees 0..n
Pmn_d_z : (m+1, n+1) array
Derivatives for all orders 0..m and degrees 0..n
See Also
--------
clpmn: associated Legendre functions of the first kind for complex z
Notes
-----
In the interval (-1, 1), Ferrer's function of the first kind is
returned. The phase convention used for the intervals (1, inf)
and (-inf, -1) is such that the result is always real.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions
https://dlmf.nist.gov/14.3
"""
if not isscalar(m) or (abs(m) > n):
raise ValueError("m must be <= n.")
if not isscalar(n) or (n < 0):
raise ValueError("n must be a non-negative integer.")
if not isscalar(z):
raise ValueError("z must be scalar.")
if iscomplex(z):
raise ValueError("Argument must be real. Use clpmn instead.")
if (m < 0):
mp = -m
mf, nf = mgrid[0:mp+1, 0:n+1]
with ufuncs.errstate(all='ignore'):
if abs(z) < 1:
# Ferrer function; DLMF 14.9.3
fixarr = where(mf > nf, 0.0,
(-1)**mf * gamma(nf-mf+1) / gamma(nf+mf+1))
else:
# Match to clpmn; DLMF 14.9.13
fixarr = where(mf > nf, 0.0, gamma(nf-mf+1) / gamma(nf+mf+1))
else:
mp = m
p, pd = specfun.lpmn(mp, n, z)
if (m < 0):
p = p * fixarr
pd = pd * fixarr
return p, pd
def clpmn(m, n, z, type=3):
"""Associated Legendre function of the first kind for complex arguments.
Computes the associated Legendre function of the first kind of order m and
degree n, ``Pmn(z)`` = :math:`P_n^m(z)`, and its derivative, ``Pmn'(z)``.
Returns two arrays of size ``(m+1, n+1)`` containing ``Pmn(z)`` and
``Pmn'(z)`` for all orders from ``0..m`` and degrees from ``0..n``.
Parameters
----------
m : int
``|m| <= n``; the order of the Legendre function.
n : int
where ``n >= 0``; the degree of the Legendre function. Often
called ``l`` (lower case L) in descriptions of the associated
Legendre function
z : float or complex
Input value.
type : int, optional
takes values 2 or 3
2: cut on the real axis ``|x| > 1``
3: cut on the real axis ``-1 < x < 1`` (default)
Returns
-------
Pmn_z : (m+1, n+1) array
Values for all orders ``0..m`` and degrees ``0..n``
Pmn_d_z : (m+1, n+1) array
Derivatives for all orders ``0..m`` and degrees ``0..n``
See Also
--------
lpmn: associated Legendre functions of the first kind for real z
Notes
-----
By default, i.e. for ``type=3``, phase conventions are chosen according
to [1]_ such that the function is analytic. The cut lies on the interval
(-1, 1). Approaching the cut from above or below in general yields a phase
factor with respect to Ferrer's function of the first kind
(cf. `lpmn`).
For ``type=2`` a cut at ``|x| > 1`` is chosen. Approaching the real values
on the interval (-1, 1) in the complex plane yields Ferrer's function
of the first kind.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] NIST Digital Library of Mathematical Functions
https://dlmf.nist.gov/14.21
"""
if not isscalar(m) or (abs(m) > n):
raise ValueError("m must be <= n.")
if not isscalar(n) or (n < 0):
raise ValueError("n must be a non-negative integer.")
if not isscalar(z):
raise ValueError("z must be scalar.")
if not(type == 2 or type == 3):
raise ValueError("type must be either 2 or 3.")
if (m < 0):
mp = -m
mf, nf = mgrid[0:mp+1, 0:n+1]
with ufuncs.errstate(all='ignore'):
if type == 2:
fixarr = where(mf > nf, 0.0,
(-1)**mf * gamma(nf-mf+1) / gamma(nf+mf+1))
else:
fixarr = where(mf > nf, 0.0, gamma(nf-mf+1) / gamma(nf+mf+1))
else:
mp = m
p, pd = specfun.clpmn(mp, n, real(z), imag(z), type)
if (m < 0):
p = p * fixarr
pd = pd * fixarr
return p, pd
def lqmn(m, n, z):
"""Sequence of associated Legendre functions of the second kind.
Computes the associated Legendre function of the second kind of order m and
degree n, ``Qmn(z)`` = :math:`Q_n^m(z)`, and its derivative, ``Qmn'(z)``.
Returns two arrays of size ``(m+1, n+1)`` containing ``Qmn(z)`` and
``Qmn'(z)`` for all orders from ``0..m`` and degrees from ``0..n``.
Parameters
----------
m : int
``|m| <= n``; the order of the Legendre function.
n : int
where ``n >= 0``; the degree of the Legendre function. Often
called ``l`` (lower case L) in descriptions of the associated
Legendre function
z : complex
Input value.
Returns
-------
Qmn_z : (m+1, n+1) array
Values for all orders 0..m and degrees 0..n
Qmn_d_z : (m+1, n+1) array
Derivatives for all orders 0..m and degrees 0..n
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(m) or (m < 0):
raise ValueError("m must be a non-negative integer.")
if not isscalar(n) or (n < 0):
raise ValueError("n must be a non-negative integer.")
if not isscalar(z):
raise ValueError("z must be scalar.")
m = int(m)
n = int(n)
# Ensure neither m nor n == 0
mm = max(1, m)
nn = max(1, n)
if iscomplex(z):
q, qd = specfun.clqmn(mm, nn, z)
else:
q, qd = specfun.lqmn(mm, nn, z)
return q[:(m+1), :(n+1)], qd[:(m+1), :(n+1)]
def bernoulli(n):
"""Bernoulli numbers B0..Bn (inclusive).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(n) or (n < 0):
raise ValueError("n must be a non-negative integer.")
n = int(n)
if (n < 2):
n1 = 2
else:
n1 = n
return specfun.bernob(int(n1))[:(n+1)]
def euler(n):
"""Euler numbers E(0), E(1), ..., E(n).
The Euler numbers [1]_ are also known as the secant numbers.
Because ``euler(n)`` returns floating point values, it does not give
exact values for large `n`. The first inexact value is E(22).
Parameters
----------
n : int
The highest index of the Euler number to be returned.
Returns
-------
ndarray
The Euler numbers [E(0), E(1), ..., E(n)].
The odd Euler numbers, which are all zero, are included.
References
----------
.. [1] Sequence A122045, The On-Line Encyclopedia of Integer Sequences,
https://oeis.org/A122045
.. [2] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
Examples
--------
>>> from scipy.special import euler
>>> euler(6)
array([ 1., 0., -1., 0., 5., 0., -61.])
>>> euler(13).astype(np.int64)
array([ 1, 0, -1, 0, 5, 0, -61,
0, 1385, 0, -50521, 0, 2702765, 0])
>>> euler(22)[-1] # Exact value of E(22) is -69348874393137901.
-69348874393137976.0
"""
if not isscalar(n) or (n < 0):
raise ValueError("n must be a non-negative integer.")
n = int(n)
if (n < 2):
n1 = 2
else:
n1 = n
return specfun.eulerb(n1)[:(n+1)]
def lpn(n, z):
"""Legendre function of the first kind.
Compute sequence of Legendre functions of the first kind (polynomials),
Pn(z) and derivatives for all degrees from 0 to n (inclusive).
See also special.legendre for polynomial class.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(n) and isscalar(z)):
raise ValueError("arguments must be scalars.")
n = _nonneg_int_or_fail(n, 'n', strict=False)
if (n < 1):
n1 = 1
else:
n1 = n
if iscomplex(z):
pn, pd = specfun.clpn(n1, z)
else:
pn, pd = specfun.lpn(n1, z)
return pn[:(n+1)], pd[:(n+1)]
def lqn(n, z):
"""Legendre function of the second kind.
Compute sequence of Legendre functions of the second kind, Qn(z) and
derivatives for all degrees from 0 to n (inclusive).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(n) and isscalar(z)):
raise ValueError("arguments must be scalars.")
n = _nonneg_int_or_fail(n, 'n', strict=False)
if (n < 1):
n1 = 1
else:
n1 = n
if iscomplex(z):
qn, qd = specfun.clqn(n1, z)
else:
qn, qd = specfun.lqnb(n1, z)
return qn[:(n+1)], qd[:(n+1)]
def ai_zeros(nt):
"""
Compute `nt` zeros and values of the Airy function Ai and its derivative.
Computes the first `nt` zeros, `a`, of the Airy function Ai(x);
first `nt` zeros, `ap`, of the derivative of the Airy function Ai'(x);
the corresponding values Ai(a');
and the corresponding values Ai'(a).
Parameters
----------
nt : int
Number of zeros to compute
Returns
-------
a : ndarray
First `nt` zeros of Ai(x)
ap : ndarray
First `nt` zeros of Ai'(x)
ai : ndarray
Values of Ai(x) evaluated at first `nt` zeros of Ai'(x)
aip : ndarray
Values of Ai'(x) evaluated at first `nt` zeros of Ai(x)
Examples
--------
>>> from scipy import special
>>> a, ap, ai, aip = special.ai_zeros(3)
>>> a
array([-2.33810741, -4.08794944, -5.52055983])
>>> ap
array([-1.01879297, -3.24819758, -4.82009921])
>>> ai
array([ 0.53565666, -0.41901548, 0.38040647])
>>> aip
array([ 0.70121082, -0.80311137, 0.86520403])
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
kf = 1
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be a positive integer scalar.")
return specfun.airyzo(nt, kf)
def bi_zeros(nt):
"""
Compute `nt` zeros and values of the Airy function Bi and its derivative.
Computes the first `nt` zeros, b, of the Airy function Bi(x);
first `nt` zeros, b', of the derivative of the Airy function Bi'(x);
the corresponding values Bi(b');
and the corresponding values Bi'(b).
Parameters
----------
nt : int
Number of zeros to compute
Returns
-------
b : ndarray
First `nt` zeros of Bi(x)
bp : ndarray
First `nt` zeros of Bi'(x)
bi : ndarray
Values of Bi(x) evaluated at first `nt` zeros of Bi'(x)
bip : ndarray
Values of Bi'(x) evaluated at first `nt` zeros of Bi(x)
Examples
--------
>>> from scipy import special
>>> b, bp, bi, bip = special.bi_zeros(3)
>>> b
array([-1.17371322, -3.2710933 , -4.83073784])
>>> bp
array([-2.29443968, -4.07315509, -5.51239573])
>>> bi
array([-0.45494438, 0.39652284, -0.36796916])
>>> bip
array([ 0.60195789, -0.76031014, 0.83699101])
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
kf = 2
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be a positive integer scalar.")
return specfun.airyzo(nt, kf)
def lmbda(v, x):
r"""Jahnke-Emden Lambda function, Lambdav(x).
This function is defined as [2]_,
.. math:: \Lambda_v(x) = \Gamma(v+1) \frac{J_v(x)}{(x/2)^v},
where :math:`\Gamma` is the gamma function and :math:`J_v` is the
Bessel function of the first kind.
Parameters
----------
v : float
Order of the Lambda function
x : float
Value at which to evaluate the function and derivatives
Returns
-------
vl : ndarray
Values of Lambda_vi(x), for vi=v-int(v), vi=1+v-int(v), ..., vi=v.
dl : ndarray
Derivatives Lambda_vi'(x), for vi=v-int(v), vi=1+v-int(v), ..., vi=v.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
.. [2] Jahnke, E. and Emde, F. "Tables of Functions with Formulae and
Curves" (4th ed.), Dover, 1945
"""
if not (isscalar(v) and isscalar(x)):
raise ValueError("arguments must be scalars.")
if (v < 0):
raise ValueError("argument must be > 0.")
n = int(v)
v0 = v - n
if (n < 1):
n1 = 1
else:
n1 = n
v1 = n1 + v0
if (v != floor(v)):
vm, vl, dl = specfun.lamv(v1, x)
else:
vm, vl, dl = specfun.lamn(v1, x)
return vl[:(n+1)], dl[:(n+1)]
def pbdv_seq(v, x):
"""Parabolic cylinder functions Dv(x) and derivatives.
Parameters
----------
v : float
Order of the parabolic cylinder function
x : float
Value at which to evaluate the function and derivatives
Returns
-------
dv : ndarray
Values of D_vi(x), for vi=v-int(v), vi=1+v-int(v), ..., vi=v.
dp : ndarray
Derivatives D_vi'(x), for vi=v-int(v), vi=1+v-int(v), ..., vi=v.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 13.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(v) and isscalar(x)):
raise ValueError("arguments must be scalars.")
n = int(v)
v0 = v-n
if (n < 1):
n1 = 1
else:
n1 = n
v1 = n1 + v0
dv, dp, pdf, pdd = specfun.pbdv(v1, x)
return dv[:n1+1], dp[:n1+1]
def pbvv_seq(v, x):
"""Parabolic cylinder functions Vv(x) and derivatives.
Parameters
----------
v : float
Order of the parabolic cylinder function
x : float
Value at which to evaluate the function and derivatives
Returns
-------
dv : ndarray
Values of V_vi(x), for vi=v-int(v), vi=1+v-int(v), ..., vi=v.
dp : ndarray
Derivatives V_vi'(x), for vi=v-int(v), vi=1+v-int(v), ..., vi=v.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 13.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(v) and isscalar(x)):
raise ValueError("arguments must be scalars.")
n = int(v)
v0 = v-n
if (n <= 1):
n1 = 1
else:
n1 = n
v1 = n1 + v0
dv, dp, pdf, pdd = specfun.pbvv(v1, x)
return dv[:n1+1], dp[:n1+1]
def pbdn_seq(n, z):
"""Parabolic cylinder functions Dn(z) and derivatives.
Parameters
----------
n : int
Order of the parabolic cylinder function
z : complex
Value at which to evaluate the function and derivatives
Returns
-------
dv : ndarray
Values of D_i(z), for i=0, ..., i=n.
dp : ndarray
Derivatives D_i'(z), for i=0, ..., i=n.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996, chapter 13.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(n) and isscalar(z)):
raise ValueError("arguments must be scalars.")
if (floor(n) != n):
raise ValueError("n must be an integer.")
if (abs(n) <= 1):
n1 = 1
else:
n1 = n
cpb, cpd = specfun.cpbdn(n1, z)
return cpb[:n1+1], cpd[:n1+1]
def ber_zeros(nt):
"""Compute nt zeros of the Kelvin function ber(x).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 1)
def bei_zeros(nt):
"""Compute nt zeros of the Kelvin function bei(x).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 2)
def ker_zeros(nt):
"""Compute nt zeros of the Kelvin function ker(x).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 3)
def kei_zeros(nt):
"""Compute nt zeros of the Kelvin function kei(x).
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 4)
def berp_zeros(nt):
"""Compute nt zeros of the Kelvin function ber'(x).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 5)
def beip_zeros(nt):
"""Compute nt zeros of the Kelvin function bei'(x).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 6)
def kerp_zeros(nt):
"""Compute nt zeros of the Kelvin function ker'(x).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 7)
def keip_zeros(nt):
"""Compute nt zeros of the Kelvin function kei'(x).
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return specfun.klvnzo(nt, 8)
def kelvin_zeros(nt):
"""Compute nt zeros of all Kelvin functions.
Returned in a length-8 tuple of arrays of length nt. The tuple contains
the arrays of zeros of (ber, bei, ker, kei, ber', bei', ker', kei').
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not isscalar(nt) or (floor(nt) != nt) or (nt <= 0):
raise ValueError("nt must be positive integer scalar.")
return (specfun.klvnzo(nt, 1),
specfun.klvnzo(nt, 2),
specfun.klvnzo(nt, 3),
specfun.klvnzo(nt, 4),
specfun.klvnzo(nt, 5),
specfun.klvnzo(nt, 6),
specfun.klvnzo(nt, 7),
specfun.klvnzo(nt, 8))
def pro_cv_seq(m, n, c):
"""Characteristic values for prolate spheroidal wave functions.
Compute a sequence of characteristic values for the prolate
spheroidal wave functions for mode m and n'=m..n and spheroidal
parameter c.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(m) and isscalar(n) and isscalar(c)):
raise ValueError("Arguments must be scalars.")
if (n != floor(n)) or (m != floor(m)):
raise ValueError("Modes must be integers.")
if (n-m > 199):
raise ValueError("Difference between n and m is too large.")
maxL = n-m+1
return specfun.segv(m, n, c, 1)[1][:maxL]
def obl_cv_seq(m, n, c):
"""Characteristic values for oblate spheroidal wave functions.
Compute a sequence of characteristic values for the oblate
spheroidal wave functions for mode m and n'=m..n and spheroidal
parameter c.
References
----------
.. [1] Zhang, Shanjie and Jin, Jianming. "Computation of Special
Functions", John Wiley and Sons, 1996.
https://people.sc.fsu.edu/~jburkardt/f_src/special_functions/special_functions.html
"""
if not (isscalar(m) and isscalar(n) and isscalar(c)):
raise ValueError("Arguments must be scalars.")
if (n != floor(n)) or (m != floor(m)):
raise ValueError("Modes must be integers.")
if (n-m > 199):
raise ValueError("Difference between n and m is too large.")
maxL = n-m+1
return specfun.segv(m, n, c, -1)[1][:maxL]
def ellipk(m):
r"""Complete elliptic integral of the first kind.
This function is defined as
.. math:: K(m) = \int_0^{\pi/2} [1 - m \sin(t)^2]^{-1/2} dt
Parameters
----------
m : array_like
The parameter of the elliptic integral.
Returns
-------
K : array_like
Value of the elliptic integral.
Notes
-----
For more precision around point m = 1, use `ellipkm1`, which this
function calls.
The parameterization in terms of :math:`m` follows that of section
17.2 in [1]_. Other parameterizations in terms of the
complementary parameter :math:`1 - m`, modular angle
:math:`\sin^2(\alpha) = m`, or modulus :math:`k^2 = m` are also
used, so be careful that you choose the correct parameter.
See Also
--------
ellipkm1 : Complete elliptic integral of the first kind around m = 1
ellipkinc : Incomplete elliptic integral of the first kind
ellipe : Complete elliptic integral of the second kind
ellipeinc : Incomplete elliptic integral of the second kind
References
----------
.. [1] Milton Abramowitz and Irene A. Stegun, eds.
Handbook of Mathematical Functions with Formulas,
Graphs, and Mathematical Tables. New York: Dover, 1972.
"""
return ellipkm1(1 - asarray(m))
def comb(N, k, exact=False, repetition=False):
"""The number of combinations of N things taken k at a time.
This is often expressed as "N choose k".
Parameters
----------
N : int, ndarray
Number of things.
k : int, ndarray
Number of elements taken.
exact : bool, optional
If `exact` is False, then floating point precision is used, otherwise
exact long integer is computed.
repetition : bool, optional
If `repetition` is True, then the number of combinations with
repetition is computed.
Returns
-------
val : int, float, ndarray
The total number of combinations.
See Also
--------
binom : Binomial coefficient ufunc
Notes
-----
- Array arguments accepted only for exact=False case.
- If k > N, N < 0, or k < 0, then a 0 is returned.
Examples
--------
>>> from scipy.special import comb
>>> k = np.array([3, 4])
>>> n = np.array([10, 10])
>>> comb(n, k, exact=False)
array([ 120., 210.])
>>> comb(10, 3, exact=True)
120L
>>> comb(10, 3, exact=True, repetition=True)
220L
"""
if repetition:
return comb(N + k - 1, k, exact)
if exact:
return _comb_int(N, k)
else:
k, N = asarray(k), asarray(N)
cond = (k <= N) & (N >= 0) & (k >= 0)
vals = binom(N, k)
if isinstance(vals, np.ndarray):
vals[~cond] = 0
elif not cond:
vals = np.float64(0)
return vals
def perm(N, k, exact=False):
"""Permutations of N things taken k at a time, i.e., k-permutations of N.
It's also known as "partial permutations".
Parameters
----------
N : int, ndarray
Number of things.
k : int, ndarray
Number of elements taken.
exact : bool, optional
If `exact` is False, then floating point precision is used, otherwise
exact long integer is computed.
Returns
-------
val : int, ndarray
The number of k-permutations of N.
Notes
-----
- Array arguments accepted only for exact=False case.
- If k > N, N < 0, or k < 0, then a 0 is returned.
Examples
--------
>>> from scipy.special import perm
>>> k = np.array([3, 4])
>>> n = np.array([10, 10])
>>> perm(n, k)
array([ 720., 5040.])
>>> perm(10, 3, exact=True)
720
"""
if exact:
if (k > N) or (N < 0) or (k < 0):
return 0
val = 1
for i in xrange(N - k + 1, N + 1):
val *= i
return val
else:
k, N = asarray(k), asarray(N)
cond = (k <= N) & (N >= 0) & (k >= 0)
vals = poch(N - k + 1, k)
if isinstance(vals, np.ndarray):
vals[~cond] = 0
elif not cond:
vals = np.float64(0)
return vals
# https://stackoverflow.com/a/16327037
def _range_prod(lo, hi):
"""
Product of a range of numbers.
Returns the product of
lo * (lo+1) * (lo+2) * ... * (hi-2) * (hi-1) * hi
= hi! / (lo-1)!
Breaks into smaller products first for speed:
_range_prod(2, 9) = ((2*3)*(4*5))*((6*7)*(8*9))
"""
if lo + 1 < hi:
mid = (hi + lo) // 2
return _range_prod(lo, mid) * _range_prod(mid + 1, hi)
if lo == hi:
return lo
return lo * hi
def factorial(n, exact=False):
"""
The factorial of a number or array of numbers.
The factorial of non-negative integer `n` is the product of all
positive integers less than or equal to `n`::
n! = n * (n - 1) * (n - 2) * ... * 1
Parameters
----------
n : int or array_like of ints
Input values. If ``n < 0``, the return value is 0.
exact : bool, optional
If True, calculate the answer exactly using long integer arithmetic.
If False, result is approximated in floating point rapidly using the
`gamma` function.
Default is False.
Returns
-------
nf : float or int or ndarray
Factorial of `n`, as integer or float depending on `exact`.
Notes
-----
For arrays with ``exact=True``, the factorial is computed only once, for
the largest input, with each other result computed in the process.
The output dtype is increased to ``int64`` or ``object`` if necessary.
With ``exact=False`` the factorial is approximated using the gamma
function:
.. math:: n! = \\Gamma(n+1)
Examples
--------
>>> from scipy.special import factorial
>>> arr = np.array([3, 4, 5])
>>> factorial(arr, exact=False)
array([ 6., 24., 120.])
>>> factorial(arr, exact=True)
array([ 6, 24, 120])
>>> factorial(5, exact=True)
120L
"""
if exact:
if np.ndim(n) == 0:
return 0 if n < 0 else math.factorial(n)
else:
n = asarray(n)
un = np.unique(n).astype(object)
# Convert to object array of long ints if np.int can't handle size
if un[-1] > 20:
dt = object
elif un[-1] > 12:
dt = np.int64
else:
dt = np.int
out = np.empty_like(n, dtype=dt)
# Handle invalid/trivial values
un = un[un > 1]
out[n < 2] = 1
out[n < 0] = 0
# Calculate products of each range of numbers
if un.size:
val = math.factorial(un[0])
out[n == un[0]] = val
for i in xrange(len(un) - 1):
prev = un[i] + 1
current = un[i + 1]
val *= _range_prod(prev, current)
out[n == current] = val
return out
else:
n = asarray(n)
vals = gamma(n + 1)
return where(n >= 0, vals, 0)
def factorial2(n, exact=False):
"""Double factorial.
This is the factorial with every second value skipped. E.g., ``7!! = 7 * 5
* 3 * 1``. It can be approximated numerically as::
n!! = special.gamma(n/2+1)*2**((m+1)/2)/sqrt(pi) n odd
= 2**(n/2) * (n/2)! n even
Parameters
----------
n : int or array_like
Calculate ``n!!``. Arrays are only supported with `exact` set
to False. If ``n < 0``, the return value is 0.
exact : bool, optional
The result can be approximated rapidly using the gamma-formula
above (default). If `exact` is set to True, calculate the
answer exactly using integer arithmetic.
Returns
-------
nff : float or int
Double factorial of `n`, as an int or a float depending on
`exact`.
Examples
--------
>>> from scipy.special import factorial2
>>> factorial2(7, exact=False)
array(105.00000000000001)
>>> factorial2(7, exact=True)
105L
"""
if exact:
if n < -1:
return 0
if n <= 0:
return 1
val = 1
for k in xrange(n, 0, -2):
val *= k
return val
else:
n = asarray(n)
vals = zeros(n.shape, 'd')
cond1 = (n % 2) & (n >= -1)
cond2 = (1-(n % 2)) & (n >= -1)
oddn = extract(cond1, n)
evenn = extract(cond2, n)
nd2o = oddn / 2.0
nd2e = evenn / 2.0
place(vals, cond1, gamma(nd2o + 1) / sqrt(pi) * pow(2.0, nd2o + 0.5))
place(vals, cond2, gamma(nd2e + 1) * pow(2.0, nd2e))
return vals
def factorialk(n, k, exact=True):
"""Multifactorial of n of order k, n(!!...!).
This is the multifactorial of n skipping k values. For example,
factorialk(17, 4) = 17!!!! = 17 * 13 * 9 * 5 * 1
In particular, for any integer ``n``, we have
factorialk(n, 1) = factorial(n)
factorialk(n, 2) = factorial2(n)
Parameters
----------
n : int
Calculate multifactorial. If `n` < 0, the return value is 0.
k : int
Order of multifactorial.
exact : bool, optional
If exact is set to True, calculate the answer exactly using
integer arithmetic.
Returns
-------
val : int
Multifactorial of `n`.
Raises
------
NotImplementedError
Raises when exact is False
Examples
--------
>>> from scipy.special import factorialk
>>> factorialk(5, 1, exact=True)
120L
>>> factorialk(5, 3, exact=True)
10L
"""
if exact:
if n < 1-k:
return 0
if n <= 0:
return 1
val = 1
for j in xrange(n, 0, -k):
val = val*j
return val
else:
raise NotImplementedError
def zeta(x, q=None, out=None):
r"""
Riemann or Hurwitz zeta function.
Parameters
----------
x : array_like of float
Input data, must be real
q : array_like of float, optional
Input data, must be real. Defaults to Riemann zeta.
out : ndarray, optional
Output array for the computed values.
Returns
-------
out : array_like
Values of zeta(x).
Notes
-----
The two-argument version is the Hurwitz zeta function:
.. math:: \zeta(x, q) = \sum_{k=0}^{\infty} \frac{1}{(k + q)^x},
Riemann zeta function corresponds to ``q = 1``.
See Also
--------
zetac
Examples
--------
>>> from scipy.special import zeta, polygamma, factorial
Some specific values:
>>> zeta(2), np.pi**2/6
(1.6449340668482266, 1.6449340668482264)
>>> zeta(4), np.pi**4/90
(1.0823232337111381, 1.082323233711138)
Relation to the `polygamma` function:
>>> m = 3
>>> x = 1.25
>>> polygamma(m, x)
array(2.782144009188397)
>>> (-1)**(m+1) * factorial(m) * zeta(m+1, x)
2.7821440091883969
"""
if q is None:
q = 1
return _zeta(x, q, out)