On 13 February 2016 at 07:48, Nasir Haniffa wrote:
> Hi,
>
> How to get the correct answer for the problems
>
> 1. Integral( (1+x**2)**(-3/2) ,(x,-1,1) )
>
>
> 2. Integral( (1+x**2+y**2)**(-3/2) ,(x,-1,1), (y,-1,1) )
>
> Both gives 0 in sympy which is wrong.
This is a bug in current master:
>>> from sympy import Symbol, Integral
>>> x = Symbol('x')
>>> Integral( (1+x**2)**(-3/2) ,(x,-1,1) )
Integral((x**2 + 1)**(-2), (x, -1, 1))
>>> Integral( (1+x**2)**(-3/2) ,(x,-1,1) ).doit()
1/2 + pi/4
Note that -3/2 under Python 2.7 gives -2 which is not what you want so
use -S(3)/2
>>> from sympy import S
>>> Integral( (1+x**2)**(-S(3)/2) ,(x,-1,1) ).doit()
0
>>> expr = (1+x**2)**(-S(3)/2)
>>> expr.integrate((x, -1, 1))
0
Under sympy 0.7.1 I get:
>>> Integral( (1+x**2)**(-S(3)/2) ,(x,-1,1) ).doit()
Integral((x**2 + 1)**(-3/2), (x, -1, 1))
>>> Integral( (1+x**2)**(-S(3)/2) ,(x,-1,1) ).evalf()
1.41421356237310
--
Oscar
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