Status: New
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 4069 by [email protected]: series(log(x)**a*exp(-b*x), x,
x0=1, n=2) wrong result
http://code.google.com/p/sympy/issues/detail?id=4069
a, b, x = symbols('a b x', real=True)
series(log(x)**a*exp(-b*x), x, x0=1, n=2)
returns wrong result: O(log(x)**2)
@XFAIL
def test_X12():
# Look at the generalized Taylor series around x = 1
# Result => (x - 1)^a/e^b [1 - (a + 2 b) (x - 1) / 2 + O((x - 1)^2)]
#
http://www.wolframalpha.com/input/?i=Series%5BLog%5Bx%5D%5Ea*Exp%5B-b*x%5D%2C+%7Bx%2C1%2C0%7D%5D
a, b, x = symbols('a b x', real=True)
# series returns O(log(x)**2)
assert (series(log(x)**a*exp(-b*x), x, x0=1, n=2) ==
(x - 1)**a/e**b*(1 - (a + 2*b)*(x - 1)/2 + O((x - 1)**2))
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