def eval(cls, n, z): n, z = map(sympify, (n, z)) from sympy import unpolarify if n.is_integer: if n.is_nonnegative: nz = unpolarify(z) if z != nz: return polygamma(n, nz) if n.is_positive: if z is S.Half: return ( (-1) ** (n + 1) * factorial(n) * (2 ** (n + 1) - 1) * zeta(n + 1) ) if n is S.NegativeOne: return loggamma(z) else: if z.is_Number: if z is S.NaN: return S.NaN elif z is S.Infinity: if n.is_Number: if n.is_zero: return S.Infinity else: return S.Zero if n.is_zero: return S.Infinity elif z.is_Integer: if z.is_nonpositive: return S.ComplexInfinity else: if n.is_zero: return -S.EulerGamma + harmonic(z - 1, 1) elif n.is_odd: return (-1) ** (n + 1) * factorial(n) * zeta(n + 1, z) if n.is_zero: if z is S.NaN: return S.NaN elif z.is_Rational: p, q = z.as_numer_denom() # only expand for small denominators to avoid creating long expressions if q <= 5: return expand_func(polygamma(S.Zero, z, evaluate=False)) elif z in (S.Infinity, S.NegativeInfinity): return S.Infinity else: t = z.extract_multiplicatively(S.ImaginaryUnit) if t in (S.Infinity, S.NegativeInfinity): return S.Infinity
def eval(cls, n, z): n, z = list(map(sympify, (n, z))) from sympy import unpolarify if n.is_integer: if n.is_nonnegative: nz = unpolarify(z) if z != nz: return polygamma(n, nz) if n == -1: return loggamma(z) else: if z.is_Number: if z is S.NaN: return S.NaN elif z is S.Infinity: if n.is_Number: if n is S.Zero: return S.Infinity else: return S.Zero elif z.is_Integer: if z.is_nonpositive: return S.ComplexInfinity else: if n is S.Zero: return -S.EulerGamma + harmonic(z - 1, 1) elif n.is_odd: return (-1)**(n + 1)*factorial(n)*zeta(n + 1, z) if n == 0: if z is S.NaN: return S.NaN elif z.is_Rational: p, q = z.as_numer_denom() # only expand for small denominators to avoid creating long expressions if q <= 5: return expand_func(polygamma(n, z, evaluate=False)) elif z in (S.Infinity, S.NegativeInfinity): return S.Infinity else: t = z.extract_multiplicatively(S.ImaginaryUnit) if t in (S.Infinity, S.NegativeInfinity): return S.Infinity
def hypersimp(f, k): """Given combinatorial term f(k) simplify its consecutive term ratio i.e. f(k+1)/f(k). The input term can be composed of functions and integer sequences which have equivalent representation in terms of gamma special function. The algorithm performs three basic steps: 1. Rewrite all functions in terms of gamma, if possible. 2. Rewrite all occurrences of gamma in terms of products of gamma and rising factorial with integer, absolute constant exponent. 3. Perform simplification of nested fractions, powers and if the resulting expression is a quotient of polynomials, reduce their total degree. If f(k) is hypergeometric then as result we arrive with a quotient of polynomials of minimal degree. Otherwise None is returned. For more information on the implemented algorithm refer to: 1. W. Koepf, Algorithms for m-fold Hypergeometric Summation, Journal of Symbolic Computation (1995) 20, 399-417 """ f = sympify(f) g = f.subs(k, k + 1) / f g = g.rewrite(gamma) g = expand_func(g) g = powsimp(g, deep=True, combine='exp') if g.is_rational_function(k): return simplify(g, ratio=S.Infinity) else: return None