def _compute_formula(f, x, P, Q, k, m, k_max):
"""Computes the formula for f."""
from sympy.polys import roots
sol = []
for i in range(k_max + 1, k_max + m + 1):
r = f.diff(x, i).limit(x, 0) / factorial(i)
if r is S.Zero:
continue
kterm = m*k + i
res = r
p = P.subs(k, kterm)
q = Q.subs(k, kterm)
c1 = p.subs(k, 1/k).leadterm(k)[0]
c2 = q.subs(k, 1/k).leadterm(k)[0]
res *= (-c1 / c2)**k
for r, mul in roots(p, k).items():
res *= rf(-r, k)**mul
for r, mul in roots(q, k).items():
res /= rf(-r, k)**mul
sol.append((res, kterm))
return sol
def hyper_re(DE, r, k):
"""Converts a DE into a RE.
Performs the substitution:
.. math::
x^l f^j(x) \\to (k + 1 - l)_j . a_{k + j - l}
Normalises the terms so that lowest order of a term is always r(k).
Examples
========
>>> from sympy import Function, Derivative
>>> from sympy.series.formal import hyper_re
>>> from sympy.abc import x, k
>>> f, r = Function('f'), Function('r')
>>> hyper_re(-f(x) + Derivative(f(x)), r, k)
(k + 1)*r(k + 1) - r(k)
>>> hyper_re(-x*f(x) + Derivative(f(x), x, x), r, k)
(k + 2)*(k + 3)*r(k + 3) - r(k)
See Also
========
sympy.series.formal.exp_re
"""
RE = S.Zero
g = DE.atoms(Function).pop()
x = g.atoms(Symbol).pop()
mini = None
for t in Add.make_args(DE.expand()):
coeff, d = t.as_independent(g)
c, v = coeff.as_independent(x)
l = v.as_coeff_exponent(x)[1]
if isinstance(d, Derivative):
j = len(d.args[1:])
else:
j = 0
RE += c * rf(k + 1 - l, j) * r(k + j - l)
if mini is None or j - l < mini:
mini = j - l
RE = RE.subs(k, k - mini)
m = Wild('m')
return RE.collect(r(k + m))
def hyper_re(DE, r, k):
"""Converts a DE into a RE.
Performs the substitution:
.. math::
x^l f^j(x) \\to (k + 1 - l)_j . a_{k + j - l}
Normalises the terms so that lowest order of a term is always r(k).
Examples
========
>>> from sympy import Function, Derivative
>>> from sympy.series.formal import hyper_re
>>> from sympy.abc import x, k
>>> f, r = Function('f'), Function('r')
>>> hyper_re(-f(x) + Derivative(f(x)), r, k)
(k + 1)*r(k + 1) - r(k)
>>> hyper_re(-x*f(x) + Derivative(f(x), (x, 2)), r, k)
(k + 2)*(k + 3)*r(k + 3) - r(k)
See Also
========
sympy.series.formal.exp_re
"""
RE = S.Zero
g = DE.atoms(Function).pop()
x = g.atoms(Symbol).pop()
mini = None
for t in Add.make_args(DE.expand()):
coeff, d = t.as_independent(g)
c, v = coeff.as_independent(x)
l = v.as_coeff_exponent(x)[1]
if isinstance(d, Derivative):
j = d.derivative_count
else:
j = 0
RE += c * rf(k + 1 - l, j) * r(k + j - l)
if mini is None or j - l < mini:
mini = j - l
RE = RE.subs(k, k - mini)
m = Wild('m')
return RE.collect(r(k + m))
def pdf(self, *syms):
n, theta = self.n, self.theta
condi = isinstance(self.n, Integer)
if not (isinstance(syms[0], IndexedBase) or condi):
raise ValueError("Please use IndexedBase object for syms as "
"the dimension is symbolic")
term_1 = factorial(n)/rf(theta, n)
if condi:
term_2 = Mul.fromiter(theta**syms[j]/((j+1)**syms[j]*factorial(syms[j]))
for j in range(n))
cond = Eq(sum([(k + 1)*syms[k] for k in range(n)]), n)
return Piecewise((term_1 * term_2, cond), (0, True))
syms = syms[0]
j, k = symbols('j, k', positive=True, integer=True)
term_2 = Product(theta**syms[j]/((j+1)**syms[j]*factorial(syms[j])),
(j, 0, n - 1))
cond = Eq(Sum((k + 1)*syms[k], (k, 0, n - 1)), n)
return Piecewise((term_1 * term_2, cond), (0, True))
def test_rsolve_hyper():
assert rsolve_hyper([-1, -1, 1], 0, n) in [
C0 * (S.Half - S.Half * sqrt(5))**n + C1 *
(S.Half + S.Half * sqrt(5))**n,
C1 * (S.Half - S.Half * sqrt(5))**n + C0 *
(S.Half + S.Half * sqrt(5))**n,
]
assert rsolve_hyper([n**2 - 2, -2 * n - 1, 1], 0, n) in [
C0 * rf(sqrt(2), n) + C1 * rf(-sqrt(2), n),
C1 * rf(sqrt(2), n) + C0 * rf(-sqrt(2), n),
]
assert rsolve_hyper([n**2 - k, -2 * n - 1, 1], 0, n) in [
C0 * rf(sqrt(k), n) + C1 * rf(-sqrt(k), n),
C1 * rf(sqrt(k), n) + C0 * rf(-sqrt(k), n),
]
assert rsolve_hyper([2 * n * (n + 1), -n**2 - 3 * n + 2, n - 1], 0,
n) == C1 * factorial(n) + C0 * 2**n
assert rsolve_hyper(
[n + 2, -(2 * n + 3) * (17 * n**2 + 51 * n + 39), n + 1], 0, n) == None
assert rsolve_hyper([-n - 1, -1, 1], 0, n) == None
assert rsolve_hyper([-1, 1], n, n).expand() == C0 + n**2 / 2 - n / 2
assert rsolve_hyper([-1, 1], 1 + n, n).expand() == C0 + n**2 / 2 + n / 2
assert rsolve_hyper([-1, 1], 3 * (n + n**2), n).expand() == C0 + n**3 - n
assert rsolve_hyper([-a, 1], 0, n).expand() == C0 * a**n
assert rsolve_hyper(
[-a, 0, 1], 0,
n).expand() == (-1)**n * C1 * a**(n / 2) + C0 * a**(n / 2)
assert rsolve_hyper([1, 1, 1], 0, n).expand() == \
C0*(Rational(-1, 2) - sqrt(3)*I/2)**n + C1*(Rational(-1, 2) + sqrt(3)*I/2)**n
assert rsolve_hyper([1, -2 * n / a - 2 / a, 1], 0, n) is None
def _eval_nseries(self, x, n, logx):
x0 = self.args[0].limit(x, 0)
if not (x0.is_Integer and x0 <= 0):
return super(gamma, self)._eval_nseries(x, n, logx)
t = self.args[0] - x0
return (gamma(t + 1) / rf(self.args[0], -x0 + 1))._eval_nseries(x, n, logx)
def test_rf_eval_apply():
x, y = symbols('x,y')
n, k = symbols('n k', integer=True)
m = Symbol('m', integer=True, nonnegative=True)
assert rf(nan, y) is nan
assert rf(x, nan) is nan
assert unchanged(rf, x, y)
assert rf(oo, 0) == 1
assert rf(-oo, 0) == 1
assert rf(oo, 6) is oo
assert rf(-oo, 7) is -oo
assert rf(-oo, 6) is oo
assert rf(oo, -6) is oo
assert rf(-oo, -7) is oo
assert rf(-1, pi) == 0
assert rf(-5, 1 + I) == 0
assert unchanged(rf, -3, k)
assert unchanged(rf, x, Symbol('k', integer=False))
assert rf(-3, Symbol('k', integer=False)) == 0
assert rf(Symbol('x', negative=True, integer=True),
Symbol('k', integer=False)) == 0
assert rf(x, 0) == 1
assert rf(x, 1) == x
assert rf(x, 2) == x * (x + 1)
assert rf(x, 3) == x * (x + 1) * (x + 2)
assert rf(x, 5) == x * (x + 1) * (x + 2) * (x + 3) * (x + 4)
assert rf(x, -1) == 1 / (x - 1)
assert rf(x, -2) == 1 / ((x - 1) * (x - 2))
assert rf(x, -3) == 1 / ((x - 1) * (x - 2) * (x - 3))
assert rf(1, 100) == factorial(100)
assert rf(x**2 + 3 * x, 2) == (x**2 + 3 * x) * (x**2 + 3 * x + 1)
assert isinstance(rf(x**2 + 3 * x, 2), Mul)
assert rf(x**3 + x, -2) == 1 / ((x**3 + x - 1) * (x**3 + x - 2))
assert rf(Poly(x**2 + 3 * x, x),
2) == Poly(x**4 + 8 * x**3 + 19 * x**2 + 12 * x, x)
assert isinstance(rf(Poly(x**2 + 3 * x, x), 2), Poly)
raises(ValueError, lambda: rf(Poly(x**2 + 3 * x, x, y), 2))
assert rf(Poly(x**3 + x, x),
-2) == 1 / (x**6 - 9 * x**5 + 35 * x**4 - 75 * x**3 + 94 * x**2 -
66 * x + 20)
raises(ValueError, lambda: rf(Poly(x**3 + x, x, y), -2))
assert rf(x, m).is_integer is None
assert rf(n, k).is_integer is None
assert rf(n, m).is_integer is True
assert rf(n, k + pi).is_integer is False
assert rf(n, m + pi).is_integer is False
assert rf(pi, m).is_integer is False
def check(x, k, o, n):
a, b = Dummy(), Dummy()
r = lambda x, k: o(a, b).rewrite(n).subs({a: x, b: k})
for i in range(-5, 5):
for j in range(-5, 5):
assert o(i, j) == r(i, j), (o, n, i, j)
check(x, k, rf, ff)
check(x, k, rf, binomial)
check(n, k, rf, factorial)
check(x, y, rf, factorial)
check(x, y, rf, binomial)
assert rf(x, k).rewrite(ff) == ff(x + k - 1, k)
assert rf(x, k).rewrite(gamma) == Piecewise(
(gamma(k + x) / gamma(x), x > 0),
((-1)**k * gamma(1 - x) / gamma(-k - x + 1), True))
assert rf(5, k).rewrite(gamma) == gamma(k + 5) / 24
assert rf(x, k).rewrite(binomial) == factorial(k) * binomial(x + k - 1, k)
assert rf(n, k).rewrite(factorial) == Piecewise(
(factorial(k + n - 1) / factorial(n - 1), n > 0),
((-1)**k * factorial(-n) / factorial(-k - n), True))
assert rf(5, k).rewrite(factorial) == factorial(k + 4) / 24
assert rf(x, y).rewrite(factorial) == rf(x, y)
assert rf(x, y).rewrite(binomial) == rf(x, y)
import random
from mpmath import rf as mpmath_rf
for i in range(100):
x = -500 + 500 * random.random()
k = -500 + 500 * random.random()
assert (abs(mpmath_rf(x, k) - rf(x, k)) < 10**(-15))
def test_ff_eval_apply():
x, y = symbols('x,y')
n, k = symbols('n k', integer=True)
m = Symbol('m', integer=True, nonnegative=True)
assert ff(nan, y) is nan
assert ff(x, nan) is nan
assert unchanged(ff, x, y)
assert ff(oo, 0) == 1
assert ff(-oo, 0) == 1
assert ff(oo, 6) is oo
assert ff(-oo, 7) is -oo
assert ff(-oo, 6) is oo
assert ff(oo, -6) is oo
assert ff(-oo, -7) is oo
assert ff(x, 0) == 1
assert ff(x, 1) == x
assert ff(x, 2) == x * (x - 1)
assert ff(x, 3) == x * (x - 1) * (x - 2)
assert ff(x, 5) == x * (x - 1) * (x - 2) * (x - 3) * (x - 4)
assert ff(x, -1) == 1 / (x + 1)
assert ff(x, -2) == 1 / ((x + 1) * (x + 2))
assert ff(x, -3) == 1 / ((x + 1) * (x + 2) * (x + 3))
assert ff(100, 100) == factorial(100)
assert ff(2 * x**2 - 5 * x,
2) == (2 * x**2 - 5 * x) * (2 * x**2 - 5 * x - 1)
assert isinstance(ff(2 * x**2 - 5 * x, 2), Mul)
assert ff(x**2 + 3 * x,
-2) == 1 / ((x**2 + 3 * x + 1) * (x**2 + 3 * x + 2))
assert ff(Poly(2 * x**2 - 5 * x, x),
2) == Poly(4 * x**4 - 28 * x**3 + 59 * x**2 - 35 * x, x)
assert isinstance(ff(Poly(2 * x**2 - 5 * x, x), 2), Poly)
raises(ValueError, lambda: ff(Poly(2 * x**2 - 5 * x, x, y), 2))
assert ff(Poly(x**2 + 3 * x, x),
-2) == 1 / (x**4 + 12 * x**3 + 49 * x**2 + 78 * x + 40)
raises(ValueError, lambda: ff(Poly(x**2 + 3 * x, x, y), -2))
assert ff(x, m).is_integer is None
assert ff(n, k).is_integer is None
assert ff(n, m).is_integer is True
assert ff(n, k + pi).is_integer is False
assert ff(n, m + pi).is_integer is False
assert ff(pi, m).is_integer is False
assert isinstance(ff(x, x), ff)
assert ff(n, n) == factorial(n)
def check(x, k, o, n):
a, b = Dummy(), Dummy()
r = lambda x, k: o(a, b).rewrite(n).subs({a: x, b: k})
for i in range(-5, 5):
for j in range(-5, 5):
assert o(i, j) == r(i, j), (o, n)
check(x, k, ff, rf)
check(x, k, ff, gamma)
check(n, k, ff, factorial)
check(x, k, ff, binomial)
check(x, y, ff, factorial)
check(x, y, ff, binomial)
assert ff(x, k).rewrite(rf) == rf(x - k + 1, k)
assert ff(x, k).rewrite(gamma) == Piecewise(
(gamma(x + 1) / gamma(-k + x + 1), x >= 0),
((-1)**k * gamma(k - x) / gamma(-x), True))
assert ff(5, k).rewrite(gamma) == 120 / gamma(6 - k)
assert ff(n, k).rewrite(factorial) == Piecewise(
(factorial(n) / factorial(-k + n), n >= 0),
((-1)**k * factorial(k - n - 1) / factorial(-n - 1), True))
assert ff(5, k).rewrite(factorial) == 120 / factorial(5 - k)
assert ff(x, k).rewrite(binomial) == factorial(k) * binomial(x, k)
assert ff(x, y).rewrite(factorial) == ff(x, y)
assert ff(x, y).rewrite(binomial) == ff(x, y)
import random
from mpmath import ff as mpmath_ff
for i in range(100):
x = -500 + 500 * random.random()
k = -500 + 500 * random.random()
a = mpmath_ff(x, k)
b = ff(x, k)
assert (abs(a - b) < abs(a) * 10**(-15))
def _eval_nseries(self, x, n, logx):
x0 = self.args[0].limit(x, 0)
if not (x0.is_Integer and x0 <= 0):
return super(gamma, self)._eval_nseries(x, n, logx)
t = self.args[0] - x0
return (gamma(t + 1)/rf(self.args[0], -x0 + 1))._eval_nseries(x, n, logx)
def test_gammasimp():
R = Rational
# was part of test_combsimp_gamma() in test_combsimp.py
assert gammasimp(gamma(x)) == gamma(x)
assert gammasimp(gamma(x + 1) / x) == gamma(x)
assert gammasimp(gamma(x) / (x - 1)) == gamma(x - 1)
assert gammasimp(x * gamma(x)) == gamma(x + 1)
assert gammasimp((x + 1) * gamma(x + 1)) == gamma(x + 2)
assert gammasimp(gamma(x + y) * (x + y)) == gamma(x + y + 1)
assert gammasimp(x / gamma(x + 1)) == 1 / gamma(x)
assert gammasimp((x + 1)**2 / gamma(x + 2)) == (x + 1) / gamma(x + 1)
assert gammasimp(x*gamma(x) + gamma(x + 3)/(x + 2)) == \
(x + 2)*gamma(x + 1)
assert gammasimp(gamma(2 * x) * x) == gamma(2 * x + 1) / 2
assert gammasimp(gamma(2 * x) / (x - S.Half)) == 2 * gamma(2 * x - 1)
assert gammasimp(gamma(x) * gamma(1 - x)) == pi / sin(pi * x)
assert gammasimp(gamma(x) * gamma(-x)) == -pi / (x * sin(pi * x))
assert gammasimp(1/gamma(x + 3)/gamma(1 - x)) == \
sin(pi*x)/(pi*x*(x + 1)*(x + 2))
assert gammasimp(factorial(n + 2)) == gamma(n + 3)
assert gammasimp(binomial(n, k)) == \
gamma(n + 1)/(gamma(k + 1)*gamma(-k + n + 1))
assert powsimp(gammasimp(
gamma(x)*gamma(x + S.Half)*gamma(y)/gamma(x + y))) == \
2**(-2*x + 1)*sqrt(pi)*gamma(2*x)*gamma(y)/gamma(x + y)
assert gammasimp(1/gamma(x)/gamma(x - Rational(1, 3))/gamma(x + Rational(1, 3))) == \
3**(3*x - Rational(3, 2))/(2*pi*gamma(3*x - 1))
assert simplify(
gamma(S.Half + x / 2) * gamma(1 + x / 2) / gamma(1 + x) / sqrt(pi) *
2**x) == 1
assert gammasimp(gamma(Rational(-1, 4)) *
gamma(Rational(-3, 4))) == 16 * sqrt(2) * pi / 3
assert powsimp(gammasimp(gamma(2*x)/gamma(x))) == \
2**(2*x - 1)*gamma(x + S.Half)/sqrt(pi)
# issue 6792
e = (-gamma(k) * gamma(k + 2) + gamma(k + 1)**2) / gamma(k)**2
assert gammasimp(e) == -k
assert gammasimp(1 / e) == -1 / k
e = (gamma(x) + gamma(x + 1)) / gamma(x)
assert gammasimp(e) == x + 1
assert gammasimp(1 / e) == 1 / (x + 1)
e = (gamma(x) + gamma(x + 2)) * (gamma(x - 1) + gamma(x)) / gamma(x)
assert gammasimp(e) == (x**2 + x + 1) * gamma(x + 1) / (x - 1)
e = (-gamma(k) * gamma(k + 2) + gamma(k + 1)**2) / gamma(k)**2
assert gammasimp(e**2) == k**2
assert gammasimp(e**2 / gamma(k + 1)) == k / gamma(k)
a = R(1, 2) + R(1, 3)
b = a + R(1, 3)
assert gammasimp(gamma(2 * k) / gamma(k) * gamma(k + a) *
gamma(k + b)) == 3 * 2**(2 * k + 1) * 3**(
-3 * k - 2) * sqrt(pi) * gamma(3 * k + R(3, 2)) / 2
# issue 9699
assert gammasimp(
(x + 1) * factorial(x) / gamma(y)) == gamma(x + 2) / gamma(y)
assert gammasimp(rf(x + n, k) * binomial(n, k)).simplify() == Piecewise(
(gamma(n + 1) * gamma(k + n + x) /
(gamma(k + 1) * gamma(n + x) * gamma(-k + n + 1)), n > -x),
((-1)**k * gamma(n + 1) * gamma(-n - x + 1) /
(gamma(k + 1) * gamma(-k + n + 1) * gamma(-k - n - x + 1)), True))
A, B = symbols('A B', commutative=False)
assert gammasimp(e * B * A) == gammasimp(e) * B * A
# check iteration
assert gammasimp(gamma(2 * k) / gamma(k) *
gamma(-k - R(1, 2))) == (-2**(2 * k + 1) * sqrt(pi) /
(2 *
((2 * k + 1) * cos(pi * k))))
assert gammasimp(
gamma(k) * gamma(k + R(1, 3)) * gamma(k + R(2, 3)) /
gamma(k * R(3, 2))) == (3 * 2**(3 * k + 1) * 3**(-3 * k - S.Half) *
sqrt(pi) * gamma(k * R(3, 2) + S.Half) / 2)
# issue 6153
assert gammasimp(gamma(Rational(1, 4)) / gamma(Rational(5, 4))) == 4
# was part of test_combsimp() in test_combsimp.py
assert gammasimp(binomial(n + 2, k + S.Half)) == gamma(n + 3)/ \
(gamma(k + R(3, 2))*gamma(-k + n + R(5, 2)))
assert gammasimp(binomial(n + 2, k + 2.0)) == \
gamma(n + 3)/(gamma(k + 3.0)*gamma(-k + n + 1))
# issue 11548
assert gammasimp(binomial(0, x)) == sin(pi * x) / (pi * x)
e = gamma(n + Rational(1, 3)) * gamma(n + R(2, 3))
assert gammasimp(e) == e
assert gammasimp(gamma(4*n + S.Half)/gamma(2*n - R(3, 4))) == \
2**(4*n - R(5, 2))*(8*n - 3)*gamma(2*n + R(3, 4))/sqrt(pi)
i, m = symbols('i m', integer=True)
e = gamma(exp(i))
assert gammasimp(e) == e
e = gamma(m + 3)
assert gammasimp(e) == e
e = gamma(m + 1) / (gamma(i + 1) * gamma(-i + m + 1))
assert gammasimp(e) == e
p = symbols("p", integer=True, positive=True)
assert gammasimp(gamma(-p + 4)) == gamma(-p + 4)
def test_rational_products():
assert product(1 + 1/k, (k, 1, n)) == rf(2, n)/factorial(n)
