Source code for diofant.simplify.hyperexpand

"""
Expand Hypergeometric (and Meijer G) functions into named
special functions.

The algorithm for doing this uses a collection of lookup tables of
hypergeometric functions, and various of their properties, to expand
many hypergeometric functions in terms of special functions.

It is based on the following paper:
      Kelly B. Roach.  Meijer G Function Representations.
      In: Proceedings of the 1997 International Symposium on Symbolic and
      Algebraic Computation, pages 205-211, New York, 1997. ACM.

It is described in great(er) detail in the Sphinx documentation.
"""
# SUMMARY OF EXTENSIONS FOR MEIJER G FUNCTIONS
#
# o z**rho G(ap, bq; z) = G(ap + rho, bq + rho; z)
#
# o denote z*d/dz by D
#
# o It is helpful to keep in mind that ap and bq play essentially symmetric
#   roles: G(1/z) has slightly altered parameters, with ap and bq interchanged.
#
# o There are four shift operators:
#   A_J = b_J - D,     J = 1, ..., n
#   B_J = 1 - a_j + D, J = 1, ..., m
#   C_J = -b_J + D,    J = m+1, ..., q
#   D_J = a_J - 1 - D, J = n+1, ..., p
#
#   A_J, C_J increment b_J
#   B_J, D_J decrement a_J
#
# o The corresponding four inverse-shift operators are defined if there
#   is no cancellation. Thus e.g. an index a_J (upper or lower) can be
#   incremented if a_J != b_i for i = 1, ..., q.
#
# o Order reduction: if b_j - a_i is a non-negative integer, where
#   j <= m and i > n, the corresponding quotient of gamma functions reduces
#   to a polynomial. Hence the G function can be expressed using a G-function
#   of lower order.
#   Similarly if j > m and i <= n.
#
#   Secondly, there are paired index theorems [Adamchik, The evaluation of
#   integrals of Bessel functions via G-function identities]. Suppose there
#   are three parameters a, b, c, where a is an a_i, i <= n, b is a b_j,
#   j <= m and c is a denominator parameter (i.e. a_i, i > n or b_j, j > m).
#   Suppose further all three differ by integers.
#   Then the order can be reduced.
#   TODO work this out in detail.
#
# o An index quadruple is called suitable if its order cannot be reduced.
#   If there exists a sequence of shift operators transforming one index
#   quadruple into another, we say one is reachable from the other.
#
# o Deciding if one index quadruple is reachable from another is tricky. For
#   this reason, we use hand-built routines to match and instantiate formulas.
#

from collections import defaultdict
from itertools import chain, product

from .. import DIOFANT_DEBUG
from ..core import (Add, Dummy, EulerGamma, Expr, I, Integer, Mod, Mul,
                    Rational, S, Tuple, expand, expand_func, nan, oo, pi,
                    symbols, sympify, zoo)
from ..core.compatibility import default_sort_key
from ..functions import (Chi, Ci, Ei, Piecewise, Shi, Si, besseli, besselj,
                         ceiling, cos, cosh, elliptic_e, elliptic_k, erf, exp,
                         exp_polar, expint, factorial, floor, fresnelc,
                         fresnels, gamma, lerchphi, log, lowergamma,
                         polar_lift, polarify, re, rf, root, sin, sinh, sqrt,
                         unpolarify, uppergamma)
from ..functions.special.hyper import (HyperRep_asin1, HyperRep_asin2,
                                       HyperRep_atanh, HyperRep_cosasin,
                                       HyperRep_log1, HyperRep_log2,
                                       HyperRep_power1, HyperRep_power2,
                                       HyperRep_sinasin, HyperRep_sqrts1,
                                       HyperRep_sqrts2, hyper, meijerg)
from ..polys import Poly, poly
from ..printing import sstr
from ..series import residue
from ..utilities.iterables import sift
from .powsimp import powdenest
from .simplify import simplify


# function to define "buckets"


def _mod1(x):
    # TODO see if this can work as Mod(x, 1); this will require
    # different handling of the "buckets" since these need to
    # be sorted and that fails when there is a mixture of
    # integers and expressions with parameters. With the current
    # Mod behavior, Mod(k, 1) == Mod(1, 1) == 0 if k is an integer.
    # Although the sorting can be done with Basic.compare, this may
    # still require different handling of the sorted buckets.
    if x.is_Number:
        return Mod(x, 1)
    c, x = x.as_coeff_Add()
    return Mod(c, 1) + x


# leave add formulae at the top for easy reference
[docs]def add_formulae(formulae): """ Create our knowledge base. """ from ..matrices import Matrix a, b, c, z = symbols('a b c, z', cls=Dummy) def add(ap, bq, res): func = Hyper_Function(ap, bq) formulae.append(Formula(func, z, res, (a, b, c))) def addb(ap, bq, B, C, M): func = Hyper_Function(ap, bq) formulae.append(Formula(func, z, None, (a, b, c), B, C, M)) # Luke, Y. L. (1969), The Special Functions and Their Approximations, # Volume 1, section 6.2 # 0F0 add((), (), exp(z)) # 1F0 add((a, ), (), HyperRep_power1(-a, z)) # 2F1 addb((a, a - S.Half), (2*a, ), Matrix([HyperRep_power2(a, z), HyperRep_power2(a + Rational(1, 2), z)/2]), Matrix([[1, 0]]), Matrix([[(a - S.Half)*z/(1 - z), (S.Half - a)*z/(1 - z)], [a/(1 - z), a*(z - 2)/(1 - z)]])) addb((1, 1), (2, ), Matrix([HyperRep_log1(z), 1]), Matrix([[-1/z, 0]]), Matrix([[0, z/(z - 1)], [0, 0]])) addb((S.Half, 1), (Rational(3, 2), ), Matrix([HyperRep_atanh(z), 1]), Matrix([[1, 0]]), Matrix([[-Rational(1, 2), 1/(1 - z)/2], [0, 0]])) addb((S.Half, S.Half), (Rational(3, 2), ), Matrix([HyperRep_asin1(z), HyperRep_power1(-Rational(1, 2), z)]), Matrix([[1, 0]]), Matrix([[-Rational(1, 2), Rational(1, 2)], [0, z/(1 - z)/2]])) addb((a, S.Half + a), (S.Half, ), Matrix([HyperRep_sqrts1(-a, z), -HyperRep_sqrts2(-a - Rational(1, 2), z)]), Matrix([[1, 0]]), Matrix([[0, -a], [z*(-2*a - 1)/2/(1 - z), S.Half - z*(-2*a - 1)/(1 - z)]])) # A. P. Prudnikov, Yu. A. Brychkov and O. I. Marichev (1990). # Integrals and Series: More Special Functions, Vol. 3,. # Gordon and Breach Science Publisher addb([a, -a], [S.Half], Matrix([HyperRep_cosasin(a, z), HyperRep_sinasin(a, z)]), Matrix([[1, 0]]), Matrix([[0, -a], [a*z/(1 - z), 1/(1 - z)/2]])) addb([1, 1], [3*S.Half], Matrix([HyperRep_asin2(z), 1]), Matrix([[1, 0]]), Matrix([[(z - S.Half)/(1 - z), 1/(1 - z)/2], [0, 0]])) # Complete elliptic integrals K(z) and E(z), both a 2F1 function addb([S.Half, S.Half], [S.One], Matrix([elliptic_k(z), elliptic_e(z)]), Matrix([[2/pi, 0]]), Matrix([[-S.Half, -1/(2*z-2)], [-S.Half, S.Half]])) addb([-S.Half, S.Half], [S.One], Matrix([elliptic_k(z), elliptic_e(z)]), Matrix([[0, 2/pi]]), Matrix([[-S.Half, -1/(2*z-2)], [-S.Half, S.Half]])) # 3F2 addb([-S.Half, 1, 1], [S.Half, 2], Matrix([z*HyperRep_atanh(z), HyperRep_log1(z), 1]), Matrix([[-Rational(2, 3), -1/(3*z), Rational(2, 3)]]), Matrix([[Rational(1, 2), 0, z/(1 - z)/2], [0, 0, z/(z - 1)], [0, 0, 0]])) # actually the formula for 3/2 is much nicer ... addb([-S.Half, 1, 1], [2, 2], Matrix([HyperRep_power1(Rational(1, 2), z), HyperRep_log2(z), 1]), Matrix([[Rational(4, 9) - 16/(9*z), 4/(3*z), 16/(9*z)]]), Matrix([[z/2/(z - 1), 0, 0], [1/(2*(z - 1)), 0, S.Half], [0, 0, 0]])) # 1F1 addb([1], [b], Matrix([z**(1 - b) * exp(z) * lowergamma(b - 1, z), 1]), Matrix([[b - 1, 0]]), Matrix([[1 - b + z, 1], [0, 0]])) addb([a], [2*a], Matrix([z**(S.Half - a)*exp(z/2)*besseli(a - S.Half, z/2) * gamma(a + S.Half)/4**(S.Half - a), z**(S.Half - a)*exp(z/2)*besseli(a + S.Half, z/2) * gamma(a + S.Half)/4**(S.Half - a)]), Matrix([[1, 0]]), Matrix([[z/2, z/2], [z/2, (z/2 - 2*a)]])) mz = polar_lift(-1)*z addb([a], [a + 1], Matrix([mz**(-a)*a*lowergamma(a, mz), a*exp(z)]), Matrix([[1, 0]]), Matrix([[-a, 1], [0, z]])) # This one is redundant. add([-S.Half], [S.Half], exp(z) - sqrt(pi*z)*(-I)*erf(I*sqrt(z))) # Added to get nice results for Laplace transform of Fresnel functions # http://functions.wolfram.com/07.22.03.6437.01 # Basic rule # add([1], [Rational(3, 4), Rational(5, 4)], # sqrt(pi) * (cos(2*sqrt(polar_lift(-1)*z))*fresnelc(2*root(polar_lift(-1)*z,4)/sqrt(pi)) + # sin(2*sqrt(polar_lift(-1)*z))*fresnels(2*root(polar_lift(-1)*z,4)/sqrt(pi))) # / (2*root(polar_lift(-1)*z,4))) # Manually tuned rule addb([1], [Rational(3, 4), Rational(5, 4)], Matrix([ sqrt(pi)*(I*sinh(2*sqrt(z))*fresnels(2*root(z, 4)*exp(I*pi/4)/sqrt(pi)) + cosh(2*sqrt(z))*fresnelc(2*root(z, 4)*exp(I*pi/4)/sqrt(pi))) * exp(-I*pi/4)/(2*root(z, 4)), sqrt(pi)*root(z, 4)*(sinh(2*sqrt(z))*fresnelc(2*root(z, 4)*exp(I*pi/4)/sqrt(pi)) + I*cosh(2*sqrt(z))*fresnels(2*root(z, 4)*exp(I*pi/4)/sqrt(pi))) * exp(-I*pi/4)/2, 1 ]), Matrix([[1, 0, 0]]), Matrix([[-Rational(1, 4), 1, Rational(1, 4)], [ z, Rational(1, 4), 0 ], [ 0, 0, 0 ]])) # 2F2 addb([S.Half, a], [Rational(3, 2), a + 1], Matrix([a/(2*a - 1)*(-I)*sqrt(pi/z)*erf(I*sqrt(z)), a/(2*a - 1)*(polar_lift(-1)*z)**(-a) * lowergamma(a, polar_lift(-1)*z), a/(2*a - 1)*exp(z)]), Matrix([[1, -1, 0]]), Matrix([[-S.Half, 0, 1], [0, -a, 1], [0, 0, z]])) # We make a "basis" of four functions instead of three, and give EulerGamma # an extra slot (it could just be a coefficient to 1). The advantage is # that this way Polys will not see multivariate polynomials (it treats # EulerGamma as an indeterminate), which is *way* faster. addb([1, 1], [2, 2], Matrix([Ei(z) - log(z), exp(z), 1, EulerGamma]), Matrix([[1/z, 0, 0, -1/z]]), Matrix([[0, 1, -1, 0], [0, z, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]])) # 0F1 add((), (S.Half, ), cosh(2*sqrt(z))) addb([], [b], Matrix([gamma(b)*z**((1 - b)/2)*besseli(b - 1, 2*sqrt(z)), gamma(b)*z**(1 - b/2)*besseli(b, 2*sqrt(z))]), Matrix([[1, 0]]), Matrix([[0, 1], [z, (1 - b)]])) # 0F3 x = 4*root(z, 4) def fp(a, z): return besseli(a, x) + besselj(a, x) def fm(a, z): return besseli(a, x) - besselj(a, x) # TODO branching addb([], [S.Half, a, a + S.Half], Matrix([fp(2*a - 1, z), fm(2*a, z)*root(z, 4), fm(2*a - 1, z)*sqrt(z), fp(2*a, z)*z**Rational(3, 4)]) * 2**(-2*a)*gamma(2*a)*z**((1 - 2*a)/4), Matrix([[1, 0, 0, 0]]), Matrix([[0, 1, 0, 0], [0, Rational(1, 2) - a, 1, 0], [0, 0, Rational(1, 2), 1], [z, 0, 0, 1 - a]])) x = 2*root(4*z, 4)*exp_polar(I*pi/4) addb([], [a, a + S.Half, 2*a], (2*sqrt(polar_lift(-1)*z))**(1 - 2*a)*gamma(2*a)**2 * Matrix([besselj(2*a - 1, x)*besseli(2*a - 1, x), x*(besseli(2*a, x)*besselj(2*a - 1, x) - besseli(2*a - 1, x)*besselj(2*a, x)), x**2*besseli(2*a, x)*besselj(2*a, x), x**3*(besseli(2*a, x)*besselj(2*a - 1, x) + besseli(2*a - 1, x)*besselj(2*a, x))]), Matrix([[1, 0, 0, 0]]), Matrix([[0, Rational(1, 4), 0, 0], [0, (1 - 2*a)/2, -Rational(1, 2), 0], [0, 0, 1 - 2*a, Rational(1, 4)], [-32*z, 0, 0, 1 - a]])) # 1F2 addb([a], [a - S.Half, 2*a], Matrix([z**(S.Half - a)*besseli(a - S.Half, sqrt(z))**2, z**(1 - a)*besseli(a - S.Half, sqrt(z)) * besseli(a - Rational(3, 2), sqrt(z)), z**(Rational(3, 2) - a)*besseli(a - Rational(3, 2), sqrt(z))**2]), Matrix([[-gamma(a + S.Half)**2/4**(S.Half - a), 2*gamma(a - S.Half)*gamma(a + S.Half)/4**(1 - a), 0]]), Matrix([[1 - 2*a, 1, 0], [z/2, S.Half - a, S.Half], [0, z, 0]])) addb([S.Half], [b, 2 - b], pi*(1 - b)/sin(pi*b) * Matrix([besseli(1 - b, sqrt(z))*besseli(b - 1, sqrt(z)), sqrt(z)*(besseli(-b, sqrt(z))*besseli(b - 1, sqrt(z)) + besseli(1 - b, sqrt(z))*besseli(b, sqrt(z))), besseli(-b, sqrt(z))*besseli(b, sqrt(z))]), Matrix([[1, 0, 0]]), Matrix([[b - 1, Rational(1, 2), 0], [z, 0, z], [0, Rational(1, 2), -b]])) addb([Rational(1, 2)], [Rational(3, 2), Rational(3, 2)], Matrix([Shi(2*sqrt(z))/2/sqrt(z), sinh(2*sqrt(z))/2/sqrt(z), cosh(2*sqrt(z))]), Matrix([[1, 0, 0]]), Matrix([[-S.Half, S.Half, 0], [0, -S.Half, S.Half], [0, 2*z, 0]])) # FresnelS # Basic rule # add([Rational(3, 4)], [Rational(3, 2),Rational(7, 4)], 6*fresnels( exp(pi*I/4)*root(z,4)*2/sqrt(pi) ) / ( pi * (exp(pi*I/4)*root(z,4)*2/sqrt(pi))**3 ) ) # Manually tuned rule addb([Rational(3, 4)], [Rational(3, 2), Rational(7, 4)], Matrix( [ fresnels( exp( pi*I/4)*root( z, 4)*2/sqrt( pi) ) / ( pi * (exp(pi*I/4)*root(z, 4)*2/sqrt(pi))**3 ), sinh(2*sqrt(z))/sqrt(z), cosh(2*sqrt(z)) ]), Matrix([[6, 0, 0]]), Matrix([[-Rational(3, 4), Rational(1, 16), 0], [ 0, -Rational(1, 2), 1], [ 0, z, 0]])) # FresnelC # Basic rule # add([Rational(1, 4)], [Rational(1, 2),Rational(5, 4)], fresnelc( exp(pi*I/4)*root(z,4)*2/sqrt(pi) ) / ( exp(pi*I/4)*root(z,4)*2/sqrt(pi) ) ) # Manually tuned rule addb([Rational(1, 4)], [Rational(1, 2), Rational(5, 4)], Matrix( [ sqrt( pi)*exp( -I*pi/4)*fresnelc( 2*root(z, 4)*exp(I*pi/4)/sqrt(pi))/(2*root(z, 4)), cosh(2*sqrt(z)), sinh(2*sqrt(z))*sqrt(z) ]), Matrix([[1, 0, 0]]), Matrix([[-Rational(1, 4), Rational(1, 4), 0 ], [ 0, 0, 1 ], [ 0, z, Rational(1, 2)]])) # 2F3 # XXX with this five-parameter formula is pretty slow with the current # Formula.find_instantiations (creates 2!*3!*3**(2+3) ~ 3000 # instantiations ... But it's not too bad. addb([a, a + S.Half], [2*a, b, 2*a - b + 1], gamma(b)*gamma(2*a - b + 1) * (sqrt(z)/2)**(1 - 2*a) * Matrix([besseli(b - 1, sqrt(z))*besseli(2*a - b, sqrt(z)), sqrt(z)*besseli(b, sqrt(z))*besseli(2*a - b, sqrt(z)), sqrt(z)*besseli(b - 1, sqrt(z))*besseli(2*a - b + 1, sqrt(z)), besseli(b, sqrt(z))*besseli(2*a - b + 1, sqrt(z))]), Matrix([[1, 0, 0, 0]]), Matrix([[0, Rational(1, 2), Rational(1, 2), 0], [z/2, 1 - b, 0, z/2], [z/2, 0, b - 2*a, z/2], [0, Rational(1, 2), Rational(1, 2), -2*a]])) # (C/f above comment about eulergamma in the basis). addb([1, 1], [2, 2, Rational(3, 2)], Matrix([Chi(2*sqrt(z)) - log(2*sqrt(z)), cosh(2*sqrt(z)), sqrt(z)*sinh(2*sqrt(z)), 1, EulerGamma]), Matrix([[1/z, 0, 0, 0, -1/z]]), Matrix([[0, Rational(1, 2), 0, -Rational(1, 2), 0], [0, 0, 1, 0, 0], [0, z, Rational(1, 2), 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]])) # 3F3 # This is rule: http://functions.wolfram.com/07.31.03.0134.01 # Initial reason to add it was a nice solution for # integrate(erf(a*z)/z**2, z) and same for erfc and erfi. # Basic rule # add([1, 1, a], [2, 2, a+1], (a/(z*(a-1)**2)) * # (1 - (-z)**(1-a) * (gamma(a) - uppergamma(a,-z)) # - (a-1) * (EulerGamma + uppergamma(0,-z) + log(-z)) # - exp(z))) # Manually tuned rule addb([1, 1, a], [2, 2, a+1], Matrix([a*(log(-z) + expint(1, -z) + EulerGamma)/(z*(a**2 - 2*a + 1)), a*(-z)**(-a)*(gamma(a) - uppergamma(a, -z))/(a - 1)**2, a*exp(z)/(a**2 - 2*a + 1), a/(z*(a**2 - 2*a + 1))]), Matrix([[1-a, 1, -1/z, 1]]), Matrix([[-1, 0, -1/z, 1], [0, -a, 1, 0], [0, 0, z, 0], [0, 0, 0, -1]]))
def add_meijerg_formulae(formulae): from ..matrices import Matrix a, b, c, z = list(map(Dummy, 'abcz')) rho = Dummy('rho') def add(an, ap, bm, bq, B, C, M, matcher): formulae.append(MeijerFormula(an, ap, bm, bq, z, [a, b, c, rho], B, C, M, matcher)) def detect_uppergamma(func): x = func.an[0] y, z = func.bm swapped = False if not _mod1((x - y).simplify()): swapped = True (y, z) = (z, y) if _mod1((x - z).simplify()) or x - z > 0: return l = [y, x] if swapped: l = [x, y] return {rho: y, a: x - y}, G_Function([x], [], l, []) add([a + rho], [], [rho, a + rho], [], Matrix([gamma(1 - a)*z**rho*exp(z)*uppergamma(a, z), gamma(1 - a)*z**(a + rho)]), Matrix([[1, 0]]), Matrix([[rho + z, -1], [0, a + rho]]), detect_uppergamma) def detect_3113(func): """http://functions.wolfram.com/07.34.03.0984.01""" x = func.an[0] u, v, w = func.bm if _mod1((u - v).simplify()) == 0: if _mod1((v - w).simplify()) == 0: return sig = (Rational(1, 2), Rational(1, 2), Integer(0)) x1, x2, y = u, v, w else: if _mod1((x - u).simplify()) == 0: sig = (Rational(1, 2), Integer(0), Rational(1, 2)) x1, y, x2 = u, v, w else: sig = (Integer(0), Rational(1, 2), Rational(1, 2)) y, x1, x2 = u, v, w if (_mod1((x - x1).simplify()) != 0 or _mod1((x - x2).simplify()) != 0 or _mod1((x - y).simplify()) != Rational(1, 2) or x - x1 > 0 or x - x2 > 0): return return {a: x}, G_Function([x], [], [x - Rational(1, 2) + t for t in sig], []) s = sin(2*sqrt(z)) c_ = cos(2*sqrt(z)) S_ = Si(2*sqrt(z)) - pi/2 C = Ci(2*sqrt(z)) add([a], [], [a, a, a - Rational(1, 2)], [], Matrix([sqrt(pi)*z**(a - Rational(1, 2))*(c_*S_ - s*C), sqrt(pi)*z**a*(s*S_ + c_*C), sqrt(pi)*z**a]), Matrix([[-2, 0, 0]]), Matrix([[a - Rational(1, 2), -1, 0], [z, a, Rational(1, 2)], [0, 0, a]]), detect_3113) def make_simp(z): """ Create a function that simplifies rational functions in ``z``. """ def simp(expr): """ Efficiently simplify the rational function ``expr``. """ numer, denom = expr.as_numer_denom() c, numer, denom = poly(numer, z).cancel(poly(denom, z)) return c * numer.as_expr() / denom.as_expr() return simp def debug(*args): if DIOFANT_DEBUG: for a in args: print(a, end="") print() class Hyper_Function(Expr): """ A generalized hypergeometric function. """ def __new__(cls, ap, bq): obj = super().__new__(cls) obj.ap = Tuple(*list(map(expand, ap))) obj.bq = Tuple(*list(map(expand, bq))) return obj @property def args(self): return self.ap, self.bq @property def sizes(self): return len(self.ap), len(self.bq) @property def gamma(self): """ Number of upper parameters that are negative integers This is a transformation invariant. """ return sum(bool(x.is_integer and x.is_negative) for x in self.ap) def _hashable_content(self): return super()._hashable_content() + (self.ap, self.bq) def __call__(self, arg): return hyper(self.ap, self.bq, arg) def build_invariants(self): """ Compute the invariant vector. The invariant vector is: (gamma, ((s1, n1), ..., (sk, nk)), ((t1, m1), ..., (tr, mr))) where gamma is the number of integer a < 0, s1 < ... < sk nl is the number of parameters a_i congruent to sl mod 1 t1 < ... < tr ml is the number of parameters b_i congruent to tl mod 1 If the index pair contains parameters, then this is not truly an invariant, since the parameters cannot be sorted uniquely mod1. >>> ap = (Rational(1, 2), Rational(1, 3), Rational(-1, 2), -2) >>> bq = (1, 2) Here gamma = 1, k = 3, s1 = 0, s2 = 1/3, s3 = 1/2 n1 = 1, n2 = 1, n2 = 2 r = 1, t1 = 0 m1 = 2: >>> Hyper_Function(ap, bq).build_invariants() (1, ((0, 1), (1/3, 1), (1/2, 2)), ((0, 2),)) """ abuckets, bbuckets = sift(self.ap, _mod1), sift(self.bq, _mod1) def tr(bucket): bucket = list(bucket.items()) if not any(isinstance(x[0], Mod) for x in bucket): bucket.sort(key=lambda x: default_sort_key(x[0])) bucket = tuple((mod, len(values)) for mod, values in bucket if values) return bucket return self.gamma, tr(abuckets), tr(bbuckets) def difficulty(self, func): """ Estimate how many steps it takes to reach ``func`` from self. Return -1 if impossible. """ if self.gamma != func.gamma: return -1 oabuckets, obbuckets, abuckets, bbuckets = [sift(params, _mod1) for params in (self.ap, self.bq, func.ap, func.bq)] diff = 0 for bucket, obucket in [(abuckets, oabuckets), (bbuckets, obbuckets)]: for mod in set(list(bucket) + list(obucket)): if (mod not in bucket) or (mod not in obucket) \ or len(bucket[mod]) != len(obucket[mod]): return -1 l1 = list(bucket[mod]) l2 = list(obucket[mod]) l1.sort() l2.sort() for i, j in zip(l1, l2): diff += abs(i - j) return diff def _is_suitable_origin(self): """ Decide if ``self`` is a suitable origin. A function is a suitable origin iff: * none of the ai equals bj + n, with n a non-negative integer * none of the ai is zero * none of the bj is a non-positive integer Note that this gives meaningful results only when none of the indices are symbolic. """ for a in self.ap: for b in self.bq: if (a - b).is_integer and (a - b).is_negative is False: return False for a in self.ap: if a == 0: return False for b in self.bq: if b.is_integer and b.is_nonpositive: return False return True class G_Function(Expr): """ A Meijer G-function. """ def __new__(cls, an, ap, bm, bq): obj = super().__new__(cls) obj.an = Tuple(*list(map(expand, an))) obj.ap = Tuple(*list(map(expand, ap))) obj.bm = Tuple(*list(map(expand, bm))) obj.bq = Tuple(*list(map(expand, bq))) return obj @property def args(self): return self.an, self.ap, self.bm, self.bq def _hashable_content(self): return super()._hashable_content() + self.args def __call__(self, z): return meijerg(self.an, self.ap, self.bm, self.bq, z) def compute_buckets(self): """ Compute buckets for the fours sets of parameters. We guarantee that any two equal Mod objects returned are actually the same, and that the buckets are sorted by real part (an and bq descendending, bm and ap ascending). Examples ======== >>> a, b = [1, 3, 2, Rational(3, 2)], [1 + y, y, 2, y + 3] >>> G_Function(a, b, [2], [y]).compute_buckets() ({0: [3, 2, 1], 1/2: [3/2]}, {0: [2], y: [y, y + 1, y + 3]}, {0: [2]}, {y: [y]}) """ dicts = pan, pap, pbm, pbq = [defaultdict(list) for i in range(4)] for dic, lis in zip(dicts, (self.an, self.ap, self.bm, self.bq)): for x in lis: dic[_mod1(x)].append(x) for dic, flip in zip(dicts, (True, False, False, True)): for m, items in dic.items(): x0 = items[0] items.sort(key=lambda x: x - x0, reverse=flip) dic[m] = items return tuple(dict(w) for w in dicts) @property def signature(self): return len(self.an), len(self.ap), len(self.bm), len(self.bq) # Dummy variable. _x = Dummy('dummy_for_hyperexpand') class Formula: """ This class represents hypergeometric formulae. Its data members are: - z, the argument - closed_form, the closed form expression - symbols, the free symbols (parameters) in the formula - func, the function - B, C, M (see _compute_basis) >>> func = Hyper_Function((a/2, a/3 + b, (1+a)/2), (a, b, (a+b)/7)) >>> f = Formula(func, z, None, [a, b]) """ def _compute_basis(self, closed_form): """ Compute a set of functions B=(f1, ..., fn), a nxn matrix M and a 1xn matrix C such that: closed_form = C B z d/dz B = M B. """ from ..matrices import Matrix, eye, zeros afactors = [_x + a for a in self.func.ap] bfactors = [_x + b - 1 for b in self.func.bq] expr = _x*Mul(*bfactors) - self.z*Mul(*afactors) poly = Poly(expr, _x) n = poly.degree() - 1 b = [closed_form] for _ in range(n): b.append(self.z*b[-1].diff(self.z)) self.B = Matrix(b) self.C = Matrix([[1] + [0]*n]) m = eye(n) m = m.col_insert(0, zeros(n, 1)) l = poly.all_coeffs()[1:] l.reverse() self.M = m.row_insert(n, -Matrix([l])/poly.all_coeffs()[0]) def __init__(self, func, z, res, symbols, B=None, C=None, M=None): z = sympify(z) res = sympify(res) symbols = [x for x in sympify(symbols) if func.has(x)] self.z = z self.symbols = symbols self.B = B self.C = C self.M = M self.func = func # TODO with symbolic parameters, it could be advantageous # (for prettier answers) to compute a basis only *after* # instantiation if res is not None: self._compute_basis(res) @property def closed_form(self): return (self.C*self.B)[0] def find_instantiations(self, func): """ Find substitutions of the free symbols that match ``func``. Return the substitution dictionaries as a list. Note that the returned instantiations need not actually match, or be valid! """ from ..solvers import solve ap = func.ap bq = func.bq if len(ap) != len(self.func.ap) or len(bq) != len(self.func.bq): raise TypeError('Cannot instantiate other number of parameters') symbol_values = [] for a in self.symbols: if a in self.func.ap.args: symbol_values.append(ap) elif a in self.func.bq.args: symbol_values.append(bq) else: raise ValueError("At least one of the parameters of the " "formula must be equal to %s" % (a,)) base_repl = [dict(zip(self.symbols, values)) for values in product(*symbol_values)] abuckets, bbuckets = [sift(params, _mod1) for params in [ap, bq]] a_inv, b_inv = [{a: len(vals) for a, vals in bucket.items()} for bucket in [abuckets, bbuckets]] critical_values = [[0] for _ in self.symbols] result = [] _n = Dummy() for repl in base_repl: symb_a, symb_b = [sift(params, lambda x: _mod1(x.xreplace(repl))) for params in [self.func.ap, self.func.bq]] for bucket, obucket in [(abuckets, symb_a), (bbuckets, symb_b)]: for mod in set(list(bucket) + list(obucket)): if (mod not in bucket) or (mod not in obucket) \ or len(bucket[mod]) != len(obucket[mod]): break for a, vals in zip(self.symbols, critical_values): if repl[a].free_symbols: continue exprs = [expr for expr in obucket[mod] if expr.has(a)] repl0 = repl.copy() repl0[a] += _n for expr in exprs: for target in bucket[mod]: n0 = solve(expr.xreplace(repl0) - target, _n)[0][_n] if n0.free_symbols: raise ValueError("Value should not be true") vals.append(n0) else: values = [] for a, vals in zip(self.symbols, critical_values): a0 = repl[a] min_ = floor(min(vals)) max_ = ceiling(max(vals)) values.append([a0 + n for n in range(min_, max_ + 1)]) result.extend(dict(zip(self.symbols, l)) for l in product(*values)) return result class FormulaCollection: """ A collection of formulae to use as origins. """ def __init__(self): """ Doing this globally at module init time is a pain ... """ self.symbolic_formulae = defaultdict(list) self.concrete_formulae = defaultdict(dict) self.formulae = [] add_formulae(self.formulae) # Now process the formulae into a helpful form. # These dicts are indexed by (p, q). for f in self.formulae: sizes = f.func.sizes if len(f.symbols) > 0: self.symbolic_formulae[sizes].append(f) else: inv = f.func.build_invariants() self.concrete_formulae[sizes][inv] = f def lookup_origin(self, func): """ Given the suitable target ``func``, try to find an origin in our knowledge base. >>> f = FormulaCollection() >>> f.lookup_origin(Hyper_Function((), ())).closed_form E**_z >>> f.lookup_origin(Hyper_Function([1], ())).closed_form HyperRep_power1(-1, _z) >>> i = Hyper_Function([Rational(1, 4), Rational(3, 4) + 4], [S.Half]) >>> f.lookup_origin(i).closed_form HyperRep_sqrts1(-1/4, _z) """ inv = func.build_invariants() sizes = func.sizes if sizes in self.concrete_formulae and \ inv in self.concrete_formulae[sizes]: return self.concrete_formulae[sizes][inv] # We don't have a concrete formula. Try to instantiate. if sizes not in self.symbolic_formulae: return # Too bad... possible = [] for f in self.symbolic_formulae[sizes]: repls = f.find_instantiations(func) for repl in repls: func2 = f.func.xreplace(repl) if not func2._is_suitable_origin(): continue diff = func2.difficulty(func) if diff == -1: continue possible.append((diff, repl, f, func2)) # find the nearest origin possible.sort(key=lambda x: x[0]) for _, repl, f, func2 in possible: f2 = Formula(func2, f.z, None, [], f.B.subs(repl), f.C.subs(repl), f.M.subs(repl)) if not any(e.has(nan, oo, -oo, zoo) for e in [f2.B, f2.M, f2.C]): return f2 else: return class MeijerFormula: """ This class represents a Meijer G-function formula. Its data members are: - z, the argument - symbols, the free symbols (parameters) in the formula - func, the function - B, C, M (c/f ordinary Formula) """ def __init__(self, an, ap, bm, bq, z, symbols, B, C, M, matcher): an, ap, bm, bq = [Tuple(*list(map(expand, w))) for w in [an, ap, bm, bq]] self.func = G_Function(an, ap, bm, bq) self.z = z self.symbols = symbols self._matcher = matcher self.B = B self.C = C self.M = M @property def closed_form(self): return (self.C*self.B)[0] def try_instantiate(self, func): """ Try to instantiate the current formula to (almost) match func. This uses the _matcher passed on init. """ if func.signature != self.func.signature: return res = self._matcher(func) if res is not None: subs, newfunc = res return MeijerFormula(newfunc.an, newfunc.ap, newfunc.bm, newfunc.bq, self.z, [], self.B.subs(subs), self.C.subs(subs), self.M.subs(subs), None) class MeijerFormulaCollection: """ This class holds a collection of meijer g formulae. """ def __init__(self): formulae = [] add_meijerg_formulae(formulae) self.formulae = defaultdict(list) for formula in formulae: self.formulae[formula.func.signature].append(formula) self.formulae = dict(self.formulae) def lookup_origin(self, func): """ Try to find a formula that matches func. """ if func.signature not in self.formulae: return for formula in self.formulae[func.signature]: res = formula.try_instantiate(func) if res is not None: return res class Operator: """ Base class for operators to be applied to our functions. These operators are differential operators. They are by convention expressed in the variable D = z*d/dz (although this base class does not actually care). Note that when the operator is applied to an object, we typically do *not* blindly differentiate but instead use a different representation of the z*d/dz operator (see make_derivative_operator). To subclass from this, define a __init__ method that initalises a self._poly variable. This variable stores a polynomial. By convention the generator is z*d/dz, and acts to the right of all coefficients. Thus this poly x**2 + 2*z*x + 1 represents the differential operator (z*d/dz)**2 + 2*z**2*d/dz. This class is used only in the implementation of the hypergeometric function expansion algorithm. """ def apply(self, obj, op): """ Apply ``self`` to the object ``obj``, where the generator is ``op``. >>> op = Operator() >>> op._poly = Poly(x**2 + z*x + y, x) >>> op.apply(z**7, lambda f: f.diff(z)) y*z**7 + 7*z**7 + 42*z**5 """ coeffs = self._poly.all_coeffs() coeffs.reverse() diffs = [obj] for c in coeffs[1:]: diffs.append(op(diffs[-1])) r = coeffs[0]*diffs[0] for c, d in zip(coeffs[1:], diffs[1:]): r += c*d return r class MultOperator(Operator): """ Simply multiply by a "constant" """ def __init__(self, p): self._poly = Poly(p, _x) class ShiftA(Operator): """ Increment an upper index. """ def __init__(self, ai): ai = sympify(ai) if ai == 0: raise ValueError('Cannot increment zero upper index.') self._poly = Poly(_x/ai + 1, _x) def __str__(self): return '<Increment upper %s.>' % sstr(1/self._poly.all_coeffs()[0]) class ShiftB(Operator): """ Decrement a lower index. """ def __init__(self, bi): bi = sympify(bi) if bi == 1: raise ValueError('Cannot decrement unit lower index.') self._poly = Poly(_x/(bi - 1) + 1, _x) def __str__(self): return '<Decrement lower %s.>' % sstr(1/self._poly.all_coeffs()[0] + 1) class UnShiftA(Operator): """ Decrement an upper index. """ def __init__(self, ap, bq, i, z): """ Note: i counts from zero! """ ap, bq, i = list(map(sympify, [ap, bq, i])) self._ap = ap self._bq = bq self._i = i ap = list(ap) bq = list(bq) ai = ap.pop(i) - 1 if ai == 0: raise ValueError('Cannot decrement unit upper index.') m = Poly(z*ai, _x) for a in ap: m *= Poly(_x + a, _x) A = Dummy('A') n = D = Poly(ai*A - ai, A) for b in bq: n *= (D + b - 1) b0 = -n.coeff_monomial(1) if b0 == 0: raise ValueError('Cannot decrement upper index: ' 'cancels with lower') n = Poly(Poly(n.all_coeffs()[:-1], A).as_expr().subs({A: _x/ai + 1}), _x) self._poly = Poly((n - m)/b0, _x) def __str__(self): return '<Decrement upper index #%s of %s, %s.>' % (sstr(self._i), sstr(self._ap), sstr(self._bq)) class UnShiftB(Operator): """ Increment a lower index. """ def __init__(self, ap, bq, i, z): """ Note: i counts from zero! """ ap, bq, i = list(map(sympify, [ap, bq, i])) self._ap = ap self._bq = bq self._i = i ap = list(ap) bq = list(bq) bi = bq.pop(i) + 1 if bi == 0: raise ValueError('Cannot increment -1 lower index.') m = Poly(_x*(bi - 1), _x) for b in bq: m *= Poly(_x + b - 1, _x) B = Dummy('B') D = Poly((bi - 1)*B - bi + 1, B) n = Poly(z, B) for a in ap: n *= (D + a) b0 = n.coeff_monomial(1) if b0 == 0: raise ValueError('Cannot increment index: cancels with upper') n = Poly(Poly(n.all_coeffs()[:-1], B).as_expr().subs({B: _x/(bi - 1) + 1}), _x) self._poly = Poly((m - n)/b0, _x) def __str__(self): return '<Increment lower index #%s of %s, %s.>' % (sstr(self._i), sstr(self._ap), sstr(self._bq)) class MeijerShiftA(Operator): """ Increment an upper b index. """ def __init__(self, bi): bi = sympify(bi) self._poly = Poly(bi - _x, _x) def __str__(self): return '<Increment upper b=%s.>' % sstr(self._poly.all_coeffs()[1]) class MeijerShiftB(Operator): """ Decrement an upper a index. """ def __init__(self, bi): bi = sympify(bi) self._poly = Poly(1 - bi + _x, _x) def __str__(self): return '<Decrement upper a=%s.>' % sstr(1 - self._poly.all_coeffs()[1]) class MeijerShiftC(Operator): """ Increment a lower b index. """ def __init__(self, bi): bi = sympify(bi) self._poly = Poly(-bi + _x, _x) def __str__(self): return '<Increment lower b=%s.>' % sstr(-self._poly.all_coeffs()[1]) class MeijerShiftD(Operator): """ Decrement a lower a index. """ def __init__(self, bi): bi = sympify(bi) self._poly = Poly(bi - 1 - _x, _x) def __str__(self): return '<Decrement lower a=%s.>' % sstr(self._poly.all_coeffs()[1] + 1) class MeijerUnShiftA(Operator): """ Decrement an upper b index. """ def __init__(self, an, ap, bm, bq, i, z): """ Note: i counts from zero! """ an, ap, bm, bq, i = list(map(sympify, [an, ap, bm, bq, i])) self._an = an self._ap = ap self._bm = bm self._bq = bq self._i = i an = list(an) ap = list(ap) bm = list(bm) bq = list(bq) bi = bm.pop(i) - 1 m = Poly(1, _x) for b in bm: m *= Poly(b - _x, _x) for b in bq: m *= Poly(_x - b, _x) A = Dummy('A') D = Poly(bi - A, A) n = Poly(z, A) for a in an: n *= (D + 1 - a) for a in ap: n *= (-D + a - 1) b0 = n.coeff_monomial(1) if b0 == 0: raise ValueError('Cannot decrement upper b index (cancels)') n = Poly(Poly(n.all_coeffs()[:-1], A).as_expr().subs({A: bi - _x}), _x) self._poly = Poly((m - n)/b0, _x) def __str__(self): return '<Decrement upper b index #%s of %s, %s, %s, %s.>' % (sstr(self._i), sstr(self._an), sstr(self._ap), sstr(self._bm), sstr(self._bq)) class MeijerUnShiftB(Operator): """ Increment an upper a index. """ def __init__(self, an, ap, bm, bq, i, z): """ Note: i counts from zero! """ an, ap, bm, bq, i = list(map(sympify, [an, ap, bm, bq, i])) self._an = an self._ap = ap self._bm = bm self._bq = bq self._i = i an = list(an) ap = list(ap) bm = list(bm) bq = list(bq) ai = an.pop(i) + 1 m = Poly(z, _x) for a in an: m *= Poly(1 - a + _x, _x) for a in ap: m *= Poly(a - 1 - _x, _x) B = Dummy('B') D = Poly(B + ai - 1, B) n = Poly(1, B) for b in bm: n *= (-D + b) for b in bq: n *= (D - b) b0 = n.coeff_monomial(1) if b0 == 0: raise ValueError('Cannot increment upper a index (cancels)') n = Poly(Poly(n.all_coeffs()[:-1], B).as_expr().subs({B: 1 - ai + _x}), _x) self._poly = Poly((m - n)/b0, _x) def __str__(self): return '<Increment upper a index #%s of %s, %s, %s, %s.>' % (sstr(self._i), sstr(self._an), sstr(self._ap), sstr(self._bm), sstr(self._bq)) class MeijerUnShiftC(Operator): """ Decrement a lower b index. """ # XXX this is "essentially" the same as MeijerUnShiftA. This "essentially" # can be made rigorous using the functional equation G(1/z) = G'(z), # where G' denotes a G function of slightly altered parameters. # However, sorting out the details seems harder than just coding it # again. def __init__(self, an, ap, bm, bq, i, z): """ Note: i counts from zero! """ an, ap, bm, bq, i = list(map(sympify, [an, ap, bm, bq, i])) self._an = an self._ap = ap self._bm = bm self._bq = bq self._i = i an = list(an) ap = list(ap) bm = list(bm) bq = list(bq) bi = bq.pop(i) - 1 m = Poly(1, _x) for b in bm: m *= Poly(b - _x, _x) for b in bq: m *= Poly(_x - b, _x) C = Dummy('C') D = Poly(bi + C, C) n = Poly(z, C) for a in an: n *= (D + 1 - a) for a in ap: n *= (-D + a - 1) b0 = n.coeff_monomial(1) if b0 == 0: raise ValueError('Cannot decrement lower b index (cancels)') n = Poly(Poly(n.all_coeffs()[:-1], C).as_expr().subs({C: _x - bi}), _x) self._poly = Poly((m - n)/b0, _x) def __str__(self): return '<Decrement lower b index #%s of %s, %s, %s, %s.>' % (sstr(self._i), sstr(self._an), sstr(self._ap), sstr(self._bm), sstr(self._bq)) class MeijerUnShiftD(Operator): """ Increment a lower a index. """ # XXX This is essentially the same as MeijerUnShiftA. # See comment at MeijerUnShiftC. def __init__(self, an, ap, bm, bq, i, z): """ Note: i counts from zero! """ an, ap, bm, bq, i = list(map(sympify, [an, ap, bm, bq, i])) self._an = an self._ap = ap self._bm = bm self._bq = bq self._i = i an = list(an) ap = list(ap) bm = list(bm) bq = list(bq) ai = ap.pop(i) + 1 m = Poly(z, _x) for a in an: m *= Poly(1 - a + _x, _x) for a in ap: m *= Poly(a - 1 - _x, _x) B = Dummy('B') # - this is the shift operator `D_I` D = Poly(ai - 1 - B, B) n = Poly(1, B) for b in bm: n *= (-D + b) for b in bq: n *= (D - b) b0 = n.coeff_monomial(1) if b0 == 0: raise ValueError('Cannot increment lower a index (cancels)') n = Poly(Poly(n.all_coeffs()[:-1], B).as_expr().subs({B: ai - 1 - _x}), _x) self._poly = Poly((m - n)/b0, _x) def __str__(self): return '<Increment lower a index #%s of %s, %s, %s, %s.>' % (sstr(self._i), sstr(self._an), sstr(self._ap), sstr(self._bm), sstr(self._bq)) class ReduceOrder(Operator): """ Reduce Order by cancelling an upper and a lower index. """ def __new__(cls, ai, bj): """ For convenience if reduction is not possible, return None. """ ai = sympify(ai) bj = sympify(bj) n = ai - bj if not n.is_Integer or n < 0: return if bj.is_integer and bj <= 0: return expr = Operator.__new__(cls) p = Integer(1) for k in range(n): p *= (_x + bj + k)/(bj + k) expr._poly = Poly(p, _x) expr._a = ai expr._b = bj return expr @classmethod def _meijer(cls, b, a, sign): """ Cancel b + sign*s and a + sign*s This is for meijer G functions. """ b = sympify(b) a = sympify(a) n = b - a if n.is_negative or not n.is_Integer: return expr = Operator.__new__(cls) p = Integer(1) for k in range(n): p *= (sign*_x + a + k) expr._poly = Poly(p, _x) if sign == -1: expr._a = b expr._b = a else: expr._b = Add(1, a - 1, evaluate=False) expr._a = Add(1, b - 1, evaluate=False) return expr @classmethod def meijer_minus(cls, b, a): return cls._meijer(b, a, -1) @classmethod def meijer_plus(cls, a, b): return cls._meijer(1 - a, 1 - b, 1) def __str__(self): return '<Reduce order by cancelling upper %s with lower %s.>' % \ (sstr(self._a), sstr(self._b)) def _reduce_order(ap, bq, gen, key): """ Order reduction algorithm used in Hypergeometric and Meijer G """ ap = list(ap) bq = list(bq) ap.sort(key=key) bq.sort(key=key) nap = [] # we will edit bq in place operators = [] for a in ap: op = None for i in range(len(bq)): op = gen(a, bq[i]) if op is not None: bq.pop(i) break if op is None: nap.append(a) else: operators.append(op) return nap, bq, operators def reduce_order(func): """ Given the hypergeometric function ``func``, find a sequence of operators to reduces order as much as possible. Return (newfunc, [operators]), where applying the operators to the hypergeometric function newfunc yields func. Examples ======== >>> reduce_order(Hyper_Function((1, 2), (3, 4))) (Hyper_Function((1, 2), (3, 4)), []) >>> r = reduce_order(Hyper_Function([1], [1])) >>> r[0] Hyper_Function((), ()) >>> for i in r[1]: ... print(i) <Reduce order by cancelling upper 1 with lower 1.> >>> r = reduce_order(Hyper_Function((2, 4), (3, 3))) >>> r[0] Hyper_Function((2,), (3,)) >>> for i in r[1]: ... print(i) <Reduce order by cancelling upper 4 with lower 3.> """ nap, nbq, operators = _reduce_order(func.ap, func.bq, ReduceOrder, default_sort_key) return Hyper_Function(Tuple(*nap), Tuple(*nbq)), operators def reduce_order_meijer(func): """ Given the Meijer G function parameters, ``func``, find a sequence of operators that reduces order as much as possible. Return newfunc, [operators]. Examples ======== >>> reduce_order_meijer(G_Function([3, 4], [5, 6], [3, 4], [1, 2]))[0] G_Function((4, 3), (5, 6), (3, 4), (2, 1)) >>> reduce_order_meijer(G_Function([3, 4], [5, 6], [3, 4], [1, 8]))[0] G_Function((3,), (5, 6), (3, 4), (1,)) >>> reduce_order_meijer(G_Function([3, 4], [5, 6], [7, 5], [1, 5]))[0] G_Function((3,), (), (), (1,)) >>> reduce_order_meijer(G_Function([3, 4], [5, 6], [7, 5], [5, 3]))[0] G_Function((), (), (), ()) """ nan, nbq, ops1 = _reduce_order(func.an, func.bq, ReduceOrder.meijer_plus, lambda x: default_sort_key(-x)) nbm, nap, ops2 = _reduce_order(func.bm, func.ap, ReduceOrder.meijer_minus, default_sort_key) return G_Function(nan, nap, nbm, nbq), ops1 + ops2 def make_derivative_operator(M, z): """ Create a derivative operator, to be passed to Operator.apply. """ def doit(C): r = z*C.diff(z) + C*M r = r.applyfunc(make_simp(z)) return r return doit def apply_operators(obj, ops, op): """ Apply the list of operators ``ops`` to object ``obj``, substituting ``op`` for the generator. """ res = obj for o in reversed(ops): res = o.apply(res, op) return res def devise_plan(target, origin, z): """ Devise a plan (consisting of shift and un-shift operators) to be applied to the hypergeometric function ``target`` to yield ``origin``. Returns a list of operators. Nothing to do: >>> devise_plan(Hyper_Function((1, 2), ()), Hyper_Function((1, 2), ()), z) [] >>> devise_plan(Hyper_Function((), (1, 2)), Hyper_Function((), (1, 2)), z) [] Very simple plans: >>> for i in devise_plan(Hyper_Function([2], []), Hyper_Function([1], []), z): ... i <Increment upper 1.> >>> for i in devise_plan(Hyper_Function([], [2]), Hyper_Function([], [1]), z): ... i <Increment lower index #0 of [], [1].> Several buckets: >>> for i in devise_plan(Hyper_Function((1, S.Half), ()), ... Hyper_Function((2, Rational(3, 2)), ()), z): ... i <Decrement upper index #0 of [3/2, 1], [].> <Decrement upper index #0 of [2, 3/2], [].> A slightly more complicated plan: >>> for i in devise_plan(Hyper_Function((1, 3), ()), Hyper_Function((2, 2), ()), z): ... i <Increment upper 2.> <Decrement upper index #0 of [2, 2], [].> Another more complicated plan: (note that the ap have to be shifted first!) >>> for i in devise_plan(Hyper_Function([1, -1], [2]), Hyper_Function([3, -2], [4]), z): ... i <Decrement lower 3.> <Decrement lower 4.> <Decrement upper index #1 of [-1, 2], [4].> <Decrement upper index #1 of [-1, 3], [4].> <Increment upper -2.> """ abuckets, bbuckets, nabuckets, nbbuckets = [sift(params, _mod1) for params in (target.ap, target.bq, origin.ap, origin.bq)] if len(list(abuckets)) != len(list(nabuckets)) or \ len(list(bbuckets)) != len(list(nbbuckets)): raise ValueError('%s not reachable from %s' % (target, origin)) ops = [] def do_shifts(fro, to, inc, dec): ops = [] for i in range(len(fro)): if to[i] - fro[i] > 0: sh = inc ch = 1 else: sh = dec ch = -1 while to[i] != fro[i]: ops += [sh(fro, i)] fro[i] += ch return ops def do_shifts_a(nal, nbk, al, aother, bother): """ Shift us from (nal, nbk) to (al, nbk). """ return do_shifts(nal, al, lambda p, i: ShiftA(p[i]), lambda p, i: UnShiftA(p + aother, nbk + bother, i, z)) def do_shifts_b(nal, nbk, bk, aother, bother): """ Shift us from (nal, nbk) to (nal, bk). """ return do_shifts(nbk, bk, lambda p, i: UnShiftB(nal + aother, p + bother, i, z), lambda p, i: ShiftB(p[i])) for r in sorted(chain(abuckets, bbuckets), key=default_sort_key): al = () nal = () bk = () nbk = () if r in abuckets: al = abuckets[r] nal = nabuckets[r] if r in bbuckets: bk = bbuckets[r] nbk = nbbuckets[r] if len(al) != len(nal) or len(bk) != len(nbk): raise ValueError('%s not reachable from %s' % (target, origin)) al, nal, bk, nbk = [sorted(w, key=default_sort_key) for w in [al, nal, bk, nbk]] def others(dic, key): l = [] for k, value in dic.items(): if k != key: l += list(dic[k]) return l aother = others(nabuckets, r) bother = others(nbbuckets, r) if len(al) == 0: # there can be no complications, just shift the bs as we please ops += do_shifts_b([], nbk, bk, aother, bother) elif len(bk) == 0: # there can be no complications, just shift the as as we please ops += do_shifts_a(nal, [], al, aother, bother) else: namax = nal[-1] amax = al[-1] if nbk[0] - namax <= 0 or bk[0] - amax <= 0: raise ValueError('Non-suitable parameters.') if namax - amax > 0: # we are going to shift down - first do the as, then the bs ops += do_shifts_a(nal, nbk, al, aother, bother) ops += do_shifts_b(al, nbk, bk, aother, bother) else: # we are going to shift up - first do the bs, then the as ops += do_shifts_b(nal, nbk, bk, aother, bother) ops += do_shifts_a(nal, bk, al, aother, bother) nabuckets[r] = al nbbuckets[r] = bk ops.reverse() return ops def try_shifted_sum(func, z): """ Try to recognise a hypergeometric sum that starts from k > 0. """ abuckets, bbuckets = sift(func.ap, _mod1), sift(func.bq, _mod1) if len(abuckets[Integer(0)]) != 1: return r = abuckets[Integer(0)][0] if r <= 0: return if not Integer(0) in bbuckets: return l = list(bbuckets[Integer(0)]) l.sort() k = l[0] if k <= 0: return nap = list(func.ap) nap.remove(r) nbq = list(func.bq) nbq.remove(k) k -= 1 nap = [x - k for x in nap] nbq = [x - k for x in nbq] ops = [] for n in range(r - 1): ops.append(ShiftA(n + 1)) ops.reverse() fac = factorial(k)/z**k for a in nap: fac /= rf(a, k) for b in nbq: fac *= rf(b, k) ops += [MultOperator(fac)] p = 0 for n in range(k): m = z**n/factorial(n) for a in nap: m *= rf(a, n) for b in nbq: m /= rf(b, n) p += m return Hyper_Function(nap, nbq), ops, -p def try_polynomial(func, z): """ Recognise polynomial cases. Returns None if not such a case. Requires order to be fully reduced. """ abuckets, bbuckets = sift(func.ap, _mod1), sift(func.bq, _mod1) a0 = abuckets[Integer(0)] b0 = bbuckets[Integer(0)] a0.sort() b0.sort() al0 = [x for x in a0 if x <= 0] bl0 = [x for x in b0 if x <= 0] if bl0 and all(a < bl0[-1] for a in al0): return oo if not al0: return a = al0[-1] fac = 1 res = Integer(1) for n in Tuple(*range(-a)): fac *= z fac /= n + 1 for a in func.ap: fac *= a + n for b in func.bq: fac /= b + n res += fac return res def try_lerchphi(func): """ Try to find an expression for Hyper_Function ``func`` in terms of Lerch Transcendents. Return None if no such expression can be found. """ # This is actually quite simple, and is described in Roach's paper, # section 18. # We don't need to implement the reduction to polylog here, this # is handled by expand_func. from ..matrices import Matrix, zeros from ..polys import apart # First we need to figure out if the summation coefficient is a rational # function of the summation index, and construct that rational function. abuckets, bbuckets = sift(func.ap, _mod1), sift(func.bq, _mod1) paired = {} for key, value in abuckets.items(): if key != 0 and key not in bbuckets: return bvalue = bbuckets[key] paired[key] = (list(value), list(bvalue)) bbuckets.pop(key, None) if bbuckets != {}: return if not Integer(0) in abuckets: return aints, bints = paired[Integer(0)] # Account for the additional n! in denominator paired[Integer(0)] = (aints, bints + [1]) t = Dummy('t') numer = Integer(1) denom = Integer(1) for key, (avalue, bvalue) in paired.items(): if len(avalue) != len(bvalue): return # Note that since order has been reduced fully, all the b are # bigger than all the a they differ from by an integer. In particular # if there are any negative b left, this function is not well-defined. for a, b in zip(avalue, bvalue): if (a - b).is_positive: k = a - b numer *= rf(b + t, k) denom *= rf(b, k) else: k = b - a numer *= rf(a, k) denom *= rf(a + t, k) # Now do a partial fraction decomposition. # We assemble two structures: a list monomials of pairs (a, b) representing # a*t**b (b a non-negative integer), and a dict terms, where # terms[a] = [(b, c)] means that there is a term b/(t-a)**c. part = apart(numer/denom, t) args = Add.make_args(part) monomials = [] terms = defaultdict(list) for arg in args: numer, denom = arg.as_numer_denom() if not denom.has(t): p = Poly(numer, t) if not p.is_monomial: raise TypeError("p should be monomial") ((b, ), a) = p.LT() monomials += [(a/denom, b)] continue if numer.has(t): raise NotImplementedError('Need partial fraction decomposition' ' with linear denominators') indep, [dep] = denom.as_coeff_mul(t) n = 1 if dep.is_Pow: n = dep.exp dep = dep.base if dep == t: a == 0 elif dep.is_Add: a, tmp = dep.as_independent(t) b = 1 if tmp != t: b, _ = tmp.as_independent(t) if dep != b*t + a: raise NotImplementedError('unrecognised form %s' % dep) a /= b indep *= b**n else: raise NotImplementedError('unrecognised form of partial fraction') terms[a].append((numer/indep, n)) # Now that we have this information, assemble our formula. All the # monomials yield rational functions and go into one basis element. # The terms[a] are related by differentiation. If the largest exponent is # n, we need lerchphi(z, k, a) for k = 1, 2, ..., n. # deriv maps a basis to its derivative, expressed as a C(z)-linear # combination of other basis elements. deriv = {} coeffs = defaultdict(list) z = Dummy('z') monomials.sort(key=lambda x: x[1]) mon = {0: 1/(1 - z)} if monomials: for k in range(monomials[-1][1]): mon[k + 1] = z*mon[k].diff(z) for a, n in monomials: coeffs[Integer(1)].append(a*mon[n]) for a, l in terms.items(): for c, k in l: coeffs[lerchphi(z, k, a)].append(c) l.sort(key=lambda x: x[1]) for k in range(2, l[-1][1] + 1): deriv[lerchphi(z, k, a)] = [(-a, lerchphi(z, k, a)), (1, lerchphi(z, k - 1, a))] deriv[lerchphi(z, 1, a)] = [(-a, lerchphi(z, 1, a)), (1/(1 - z), Integer(1))] trans = {} for n, b in enumerate([Integer(1)] + list(deriv)): trans[b] = n basis = [expand_func(b) for (b, _) in sorted(trans.items(), key=lambda x:x[1])] B = Matrix(basis) C = Matrix([[0]*len(B)]) for b, c in coeffs.items(): C[trans[b]] = Add(*c) M = zeros(len(B)) for b, l in deriv.items(): for c, b2 in l: M[trans[b], trans[b2]] = c return Formula(func, z, None, [], B, C, M) def build_hypergeometric_formula(func): """ Create a formula object representing the hypergeometric function ``func``. """ # We know that no `ap` are negative integers, otherwise "detect poly" # would have kicked in. However, `ap` could be empty. In this case we can # use a different basis. # I'm not aware of a basis that works in all cases. from ..matrices import zeros, Matrix, eye z = Dummy('z') if func.ap: afactors = [_x + a for a in func.ap] bfactors = [_x + b - 1 for b in func.bq] expr = _x*Mul(*bfactors) - z*Mul(*afactors) poly = Poly(expr, _x) n = poly.degree() basis = [] M = zeros(n) for k in range(n): a = func.ap[0] + k basis += [hyper([a] + list(func.ap[1:]), func.bq, z)] if k < n - 1: M[k, k] = -a M[k, k + 1] = a B = Matrix(basis) C = Matrix([[1] + [0]*(n - 1)]) derivs = [eye(n)] for k in range(n): derivs.append(M*derivs[k]) l = poly.all_coeffs() l.reverse() res = [0]*n for k, c in enumerate(l): for r, d in enumerate(C*derivs[k]): res[r] += c*d for k, c in enumerate(res): M[n - 1, k] = -c/derivs[n - 1][0, n - 1]/poly.all_coeffs()[0] return Formula(func, z, None, [], B, C, M) else: # Since there are no `ap`, none of the `bq` can be non-positive # integers. basis = [] bq = list(func.bq[:]) for i in range(len(bq)): basis += [hyper([], bq, z)] bq[i] += 1 basis += [hyper([], bq, z)] B = Matrix(basis) n = len(B) C = Matrix([[1] + [0]*(n - 1)]) M = zeros(n) M[0, n - 1] = z/Mul(*func.bq) for k in range(1, n): M[k, k - 1] = func.bq[k - 1] M[k, k] = -func.bq[k - 1] return Formula(func, z, None, [], B, C, M) def hyperexpand_special(ap, bq, z): """ Try to find a closed-form expression for hyper(ap, bq, z), where ``z`` is supposed to be a "special" value, e.g. 1. This function tries various of the classical summation formulae (Gauss, Saalschuetz, etc). """ # This code is very ad-hoc. There are many clever algorithms # (notably Zeilberger's) related to this problem. # For now we just want a few simple cases to work. p, q = len(ap), len(bq) z_ = z z = unpolarify(z) if z == 0: return S.One if p == 2 and q == 1: # 2F1 a, b, c = ap + bq if z == 1: # Gauss return gamma(c - a - b)*gamma(c)/gamma(c - a)/gamma(c - b) if z == -1 and simplify(b - a + c) == 1: b, a = a, b if z == -1 and simplify(a - b + c) == 1: # Kummer if b.is_integer and b.is_negative: return 2*cos(pi*b/2)*gamma(-b)*gamma(b - a + 1) \ / gamma(-b/2)/gamma(b/2 - a + 1) else: return gamma(b/2 + 1)*gamma(b - a + 1) \ / gamma(b + 1)/gamma(b/2 - a + 1) # TODO tons of more formulae # investigate what algorithms exist return hyper(ap, bq, z_) _collection = None def _hyperexpand(func, z, ops0=[], z0=Dummy('z0'), premult=1, prem=0, rewrite='default'): """ Try to find an expression for the hypergeometric function ``func``. The result is expressed in terms of a dummy variable z0. Then it is multiplied by premult. Then ops0 is applied. premult must be a*z**prem for some a independent of z. """ z = polarify(z, subs=False) if rewrite == 'default': rewrite = 'nonrepsmall' def carryout_plan(f, ops): from ..matrices import eye C = apply_operators(f.C.subs({f.z: z0}), ops, make_derivative_operator(f.M.subs({f.z: z0}), z0)) C = apply_operators(C, ops0, make_derivative_operator(f.M.subs({f.z: z0}) + prem*eye(f.M.shape[0]), z0)) if premult == 1: C = C.applyfunc(make_simp(z0)) r = C*f.B.subs({f.z: z0})*premult # Try substitution first res = r[0].subs({z0: z}).replace(hyper, hyperexpand_special) if rewrite: res = res.rewrite(rewrite) res = powdenest(res, polar=True) if res is not nan: pass elif not r.has(hyper): res = r[0].limit(z0, unpolarify(z)) return res # TODO # The following would be possible: # *) PFD Duplication (see Kelly Roach's paper) # *) In a similar spirit, try_lerchphi() can be generalized considerably. global _collection if _collection is None: _collection = FormulaCollection() debug('Trying to expand hypergeometric function ', func) # First reduce order as much as possible. func, ops = reduce_order(func) if ops: debug(' Reduced order to ', func) else: debug(' Could not reduce order.') # Now try polynomial cases res = try_polynomial(func, z0) if res is not None: debug(' Recognised polynomial.') p = apply_operators(res, ops, lambda f: z0*f.diff(z0)) p = apply_operators(p*premult, ops0, lambda f: z0*f.diff(z0)) return unpolarify(simplify(p).subs({z0: z})) # Try to recognise a shifted sum. p = Integer(0) res = try_shifted_sum(func, z0) if res is not None: func, nops, p = res debug(' Recognised shifted sum, reduced order to ', func) ops += nops # apply the plan for poly p = apply_operators(p, ops, lambda f: z0*f.diff(z0)) p = apply_operators(p*premult, ops0, lambda f: z0*f.diff(z0)) p = unpolarify(simplify(p).subs({z0: z})) # Try special expansions early. if unpolarify(z) in [1, 0, -1]: f = build_hypergeometric_formula(func) r = carryout_plan(f, ops) + p if not r.has(hyper) and r is not nan: return r + p # Try to find a formula in our collection formula = _collection.lookup_origin(func) # Now try a lerch phi formula if formula is None: formula = try_lerchphi(func) if formula is None: debug(' Could not find an origin. ', 'Will return answer in terms of ' 'simpler hypergeometric functions.') formula = build_hypergeometric_formula(func) debug(' Found an origin: ', formula.closed_form, ' ', formula.func) # We need to find the operators that convert formula into func. ops += devise_plan(func, formula.func, z0) # Now carry out the plan. return carryout_plan(formula, ops) + p def devise_plan_meijer(fro, to, z): """ Find operators to convert G-function ``fro`` into G-function ``to``. It is assumed that fro and to have the same signatures, and that in fact any corresponding pair of parameters differs by integers, and a direct path is possible. I.e. if there are parameters a1 b1 c1 and a2 b2 c2 it is assumed that a1 can be shifted to a2, etc. The only thing this routine determines is the order of shifts to apply, nothing clever will be tried. It is also assumed that fro is suitable. Empty plan: >>> devise_plan_meijer(G_Function([1], [2], [3], [4]), ... G_Function([1], [2], [3], [4]), z) [] Very simple plans: >>> for i in devise_plan_meijer(G_Function([0], [], [], []), ... G_Function([1], [], [], []), z): ... print(i) <Increment upper a index #0 of [0], [], [], [].> >>> for i in devise_plan_meijer(G_Function([0], [], [], []), ... G_Function([-1], [], [], []), z): ... print(i) <Decrement upper a=0.> >>> for i in devise_plan_meijer(G_Function([], [1], [], []), ... G_Function([], [2], [], []), z): ... print(i) <Increment lower a index #0 of [], [1], [], [].> Slightly more complicated plans: >>> for i in devise_plan_meijer(G_Function([0], [], [], []), ... G_Function([2], [], [], []), z): ... print(i) <Increment upper a index #0 of [1], [], [], [].> <Increment upper a index #0 of [0], [], [], [].> >>> for i in devise_plan_meijer(G_Function([0], [], [0], []), ... G_Function([-1], [], [1], []), z): ... print(i) <Increment upper b=0.> <Decrement upper a=0.> Order matters: >>> for i in devise_plan_meijer(G_Function([0], [], [0], []), ... G_Function([1], [], [1], []), z): ... print(i) <Increment upper a index #0 of [0], [], [1], [].> <Increment upper b=0.> """ # TODO for now, we use the following simple heuristic: inverse-shift # when possible, shift otherwise. Give up if we cannot make progress. def try_shift(f, t, shifter, diff, counter): """ Try to apply ``shifter`` in order to bring some element in ``f`` nearer to its counterpart in ``to``. ``diff`` is +/- 1 and determines the effect of ``shifter``. Counter is a list of elements blocking the shift. Return an operator if change was possible, else None. """ for idx, (a, b) in enumerate(zip(f, t)): if ( (a - b).is_integer and (b - a)/diff > 0 and all(a != x for x in counter)): sh = shifter(idx) f[idx] += diff return sh fan = list(fro.an) fap = list(fro.ap) fbm = list(fro.bm) fbq = list(fro.bq) ops = [] change = True while change: change = False op = try_shift(fan, to.an, lambda i: MeijerUnShiftB(fan, fap, fbm, fbq, i, z), 1, fbm + fbq) if op is not None: ops += [op] change = True continue op = try_shift(fap, to.ap, lambda i: MeijerUnShiftD(fan, fap, fbm, fbq, i, z), 1, fbm + fbq) if op is not None: ops += [op] change = True continue op = try_shift(fbm, to.bm, lambda i: MeijerUnShiftA(fan, fap, fbm, fbq, i, z), -1, fan + fap) if op is not None: ops += [op] change = True continue op = try_shift(fbq, to.bq, lambda i: MeijerUnShiftC(fan, fap, fbm, fbq, i, z), -1, fan + fap) if op is not None: ops += [op] change = True continue op = try_shift(fan, to.an, lambda i: MeijerShiftB(fan[i]), -1, []) if op is not None: ops += [op] change = True continue op = try_shift(fap, to.ap, lambda i: MeijerShiftD(fap[i]), -1, []) if op is not None: ops += [op] change = True continue op = try_shift(fbm, to.bm, lambda i: MeijerShiftA(fbm[i]), 1, []) if op is not None: ops += [op] change = True continue op = try_shift(fbq, to.bq, lambda i: MeijerShiftC(fbq[i]), 1, []) if op is not None: ops += [op] change = True continue if fan != list(to.an) or fap != list(to.ap) or fbm != list(to.bm) or \ fbq != list(to.bq): raise NotImplementedError('Could not devise plan.') ops.reverse() return ops _meijercollection = None def _meijergexpand(func, z0, allow_hyper=False, rewrite='default'): """ Try to find an expression for the Meijer G function specified by the G_Function ``func``. If ``allow_hyper`` is True, then returning an expression in terms of hypergeometric functions is allowed. Currently this just does slater's theorem. """ global _meijercollection if _meijercollection is None: _meijercollection = MeijerFormulaCollection() if rewrite == 'default': rewrite = None func0 = func debug('Try to expand Meijer G function corresponding to ', func) # We will play games with analytic continuation - rather use a fresh symbol z = Dummy('z') func, ops = reduce_order_meijer(func) if ops: debug(' Reduced order to ', func) else: debug(' Could not reduce order.') # Try to find a direct formula f = _meijercollection.lookup_origin(func) if f is not None: debug(' Found a Meijer G formula: ', f.func) ops += devise_plan_meijer(f.func, func, z) # Now carry out the plan. C = apply_operators(f.C.subs({f.z: z}), ops, make_derivative_operator(f.M.subs({f.z: z}), z)) C = C.applyfunc(make_simp(z)) r = C*f.B.subs({f.z: z}) r = r[0].subs({z: z0}) return powdenest(r, polar=True) debug(" Could not find a direct formula. Trying Slater's theorem.") # TODO the following would be possible: # *) Paired Index Theorems # *) PFD Duplication # (See Kelly Roach's paper for details on either.) # # TODO Also, we tend to create combinations of gamma functions that can be # simplified. def can_do(pbm, pap): """ Test if slater applies. """ for i in pbm: if len(pbm[i]) > 1: l = 0 if i in pap: l = len(pap[i]) if l + 1 < len(pbm[i]): return False return True def do_slater(an, bm, ap, bq, z, zfinal): # zfinal is the value that will eventually be substituted for z. # We pass it to _hyperexpand to improve performance. func = G_Function(an, bm, ap, bq) _, pbm, pap, _ = func.compute_buckets() if not can_do(pbm, pap): return Integer(0), False cond = len(an) + len(ap) < len(bm) + len(bq) if len(an) + len(ap) == len(bm) + len(bq): cond = abs(z) < 1 if cond is False: return Integer(0), False res = Integer(0) for m in pbm: if len(pbm[m]) == 1: bh = pbm[m][0] fac = 1 bo = list(bm) bo.remove(bh) for bj in bo: fac *= gamma(bj - bh) for aj in an: fac *= gamma(1 + bh - aj) for bj in bq: fac /= gamma(1 + bh - bj) for aj in ap: fac /= gamma(aj - bh) nap = [1 + bh - a for a in list(an) + list(ap)] nbq = [1 + bh - b for b in list(bo) + list(bq)] k = polar_lift(Integer(-1)**(len(ap) - len(bm))) harg = k*zfinal # NOTE even though k "is" +-1, this has to be t/k instead of # t*k ... we are using polar numbers for consistency! premult = (t/k)**bh hyp = _hyperexpand(Hyper_Function(nap, nbq), harg, ops, t, premult, bh, rewrite=None) res += fac * hyp else: b_ = pbm[m][0] ki = [bi - b_ for bi in pbm[m][1:]] u = len(ki) li = [ai - b_ for ai in pap[m][:u + 1]] bo = list(bm) for b in pbm[m]: bo.remove(b) ao = list(ap) for a in pap[m][:u]: ao.remove(a) lu = li[-1] di = [l - k for (l, k) in zip(li, ki)] # We first work out the integrand: s = Dummy('s') integrand = z**s for b in bm: integrand *= gamma(b - s) for a in an: integrand *= gamma(1 - a + s) for b in bq: integrand /= gamma(1 - b + s) for a in ap: integrand /= gamma(a - s) # Now sum the finitely many residues: # XXX This speeds up some cases - is it a good idea? integrand = expand_func(integrand) for r in range(lu): resid = residue(integrand, s, b_ + r) resid = apply_operators(resid, ops, lambda f: z*f.diff(z)) res -= resid # Now the hypergeometric term. au = b_ + lu k = polar_lift(Integer(-1)**(len(ao) + len(bo) + 1)) harg = k*zfinal premult = (t/k)**au nap = [1 + au - a for a in list(an) + list(ap)] + [1] nbq = [1 + au - b for b in list(bm) + list(bq)] hyp = _hyperexpand(Hyper_Function(nap, nbq), harg, ops, t, premult, au, rewrite=None) C = Integer(-1)**(lu)/factorial(lu) for i in range(u): C *= Integer(-1)**di[i]/rf(lu - li[i] + 1, di[i]) for a in an: C *= gamma(1 - a + au) for b in bo: C *= gamma(b - au) for a in ao: C /= gamma(a - au) for b in bq: C /= gamma(1 - b + au) res += C*hyp return res, cond t = Dummy('t') slater1, cond1 = do_slater(func.an, func.bm, func.ap, func.bq, z, z0) def tr(l): return [1 - x for x in l] for op in ops: op._poly = Poly(op._poly.subs({z: 1/t, _x: -_x}), _x) slater2, cond2 = do_slater(tr(func.bm), tr(func.an), tr(func.bq), tr(func.ap), t, 1/z0) slater1 = powdenest(slater1.subs({z: z0}), polar=True) slater2 = powdenest(slater2.subs({t: 1/z0}), polar=True) if not isinstance(cond2, bool): cond2 = cond2.subs({t: 1/z}) m = func(z) if m.delta > 0 or \ (m.delta == 0 and len(m.ap) == len(m.bq) and (re(m.nu) < -1) is not False and polar_lift(z0) == polar_lift(1)): # The condition delta > 0 means that the convergence region is # connected. Any expression we find can be continued analytically # to the entire convergence region. # The conditions delta==0, p==q, re(nu) < -1 imply that G is continuous # on the positive reals, so the values at z=1 agree. if cond1 is not False: cond1 = True if cond2 is not False: cond2 = True if cond1 is True: slater1 = slater1.rewrite(rewrite or 'nonrep') else: slater1 = slater1.rewrite(rewrite or 'nonrepsmall') if cond2 is True: slater2 = slater2.rewrite(rewrite or 'nonrep') else: slater2 = slater2.rewrite(rewrite or 'nonrepsmall') if not isinstance(cond1, bool): cond1 = cond1.subs({z: z0}) if not isinstance(cond2, bool): cond2 = cond2.subs({z: z0}) def weight(expr, cond): if cond is True: c0 = 0 elif cond is False: c0 = 1 else: c0 = 2 if expr.has(oo, zoo, -oo, nan): # XXX this actually should not happen, but consider # meijerg(((0, -S.Half, 0, -S.Half, S.Half), ()), # ((0,), (-S.Half, -S.Half, -S.Half, -1)), # exp_polar(I*pi))/4 c0 = 3 return c0, expr.count(hyper), expr.count_ops() w1 = weight(slater1, cond1) w2 = weight(slater2, cond2) if min(w1, w2) <= (0, 1, oo): if w1 < w2: return slater1 else: return slater2 if max(w1[0], w2[0]) <= 1 and max(w1[1], w2[1]) <= 1: return Piecewise((slater1, cond1), (slater2, cond2), (func0(z0), True)) # We couldn't find an expression without hypergeometric functions. # TODO it would be helpful to give conditions under which the integral # is known to diverge. r = Piecewise((slater1, cond1), (slater2, cond2), (func0(z0), True)) if r.has(hyper) and not allow_hyper: debug(' Could express using hypergeometric functions, ' 'but not allowed.') if not r.has(hyper) or allow_hyper: return r return func0(z0)
[docs]def hyperexpand(f, allow_hyper=False, rewrite='default'): """ Expand hypergeometric functions. If allow_hyper is True, allow partial simplification (that is a result different from input, but still containing hypergeometric functions). Examples ======== >>> hyperexpand(hyper([], [], z)) E**z Non-hyperegeometric parts of the expression and hypergeometric expressions that are not recognised are left unchanged: >>> hyperexpand(1 + hyper([1, 1, 1], [], z)) hyper((1, 1, 1), (), z) + 1 """ f = sympify(f) def do_replace(ap, bq, z): r = _hyperexpand(Hyper_Function(ap, bq), z, rewrite=rewrite) if r is None: return hyper(ap, bq, z) else: return r def do_meijer(ap, bq, z): r = _meijergexpand(G_Function(ap[0], ap[1], bq[0], bq[1]), z, allow_hyper, rewrite=rewrite) if not r.has(nan, zoo, oo, -oo): return r return f.replace(hyper, do_replace).replace(meijerg, do_meijer)