Status: New
Owner: ----
Labels: Type-Defect Priority-Medium Series
New issue 3891 by daveb...@gmail.com: series expands functions with square
roots of squares to too high a degree
http://code.google.com/p/sympy/issues/detail?id=3891
Asking for a simple third degree expansion of a square root that includes
squares of the variable, I get an 8th degree expansion:
In [2]: from sympy import *
In [3]: x,a,b = symbols('x,a,b')
In [4]: (sqrt(a+b*x+x**2)).series(x,0,3)
Out[4]: sqrt(a)*(x**8*(-5/(128*a**4) + 35*b**2/(128*a**5)) +
x**7*(-5*b/(32*a**4) + 35*b**3/(128*a**5)) + x**6*(1/(16*a**3) -
15*b**2/(64*a**4) + 35*b**4/(256*a
**5)) + x**5*(3*b/(16*a**3) - 5*b**3/(32*a**4) + 7*b**5/(256*a**5)) +
x**4*(-1/(8*a**2) + 3*b**2/(16*a**3) - 5*b**4/(128*a**4)) +
x**3*(-b/(4*a**2) + b**3/(16*a
**3)) + x**2*(1/(2*a) - b**2/(8*a**2)) + 1 + b*x/(2*a) +
35*b*x**9/(256*a**5) + 7*x**10/(256*a**5)) + O(x**3)
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