def test_factorial_moment():
X = Poisson('X', 2)
Y = Binomial('Y', 2, S.Half)
Z = Hypergeometric('Z', 4, 2, 2)
assert factorial_moment(X, 2) == 4
assert factorial_moment(Y, 2) == S.Half
assert factorial_moment(Z, 2) == Rational(1, 3)
x, y, z, l = symbols('x y z l')
Y = Binomial('Y', 2, y)
Z = Hypergeometric('Z', 10, 2, 3)
assert factorial_moment(Y, l) == y**2*FallingFactorial(
2, l) + 2*y*(1 - y)*FallingFactorial(1, l) + (1 - y)**2*\
FallingFactorial(0, l)
assert factorial_moment(Z, l) == 7*FallingFactorial(0, l)/\
15 + 7*FallingFactorial(1, l)/15 + FallingFactorial(2, l)/15
def test_factorial_moment():
X = Poisson("X", 2)
Y = Binomial("Y", 2, S.Half)
Z = Hypergeometric("Z", 4, 2, 2)
assert factorial_moment(X, 2) == 4
assert factorial_moment(Y, 2) == S.Half
assert factorial_moment(Z, 2) == Rational(1, 3)
x, y, z, l = symbols("x y z l")
Y = Binomial("Y", 2, y)
Z = Hypergeometric("Z", 10, 2, 3)
assert factorial_moment(Y, l) == y ** 2 * FallingFactorial(2, l) + 2 * y * (
1 - y
) * FallingFactorial(1, l) + (1 - y) ** 2 * FallingFactorial(0, l)
assert (
factorial_moment(Z, l)
== 7 * FallingFactorial(0, l) / 15
+ 7 * FallingFactorial(1, l) / 15
+ FallingFactorial(2, l) / 15
)
