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# improper integral error?

Is there an alternative way to calculate this improper integral?

integral(log(x)/(x^2 - 1),x,0,infinity)

the integral is convergent to pi^2/4 but Sage says divergent.

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## 2 Answers

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With the algorithm set to mathematica_free, Sage is returning the antiderivative even though you are asking for the improper integral. You can get the improper integral by doing the following:

f=integral(log(x)/(x^2 - 1),x,algorithm='mathematica_free')
limit(f,x=oo)-limit(f,x=0)


This returns pi^2/4.

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Always try the other available "algorithms":

sage: integral(log(x)/(x^2 - 1),x,0,infinity, algorithm='mathematica_free')
-1/2*log(x + 1)*log(x) - 1/2*polylog(2, -x) - 1/2*polylog(2, -x + 1)

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## Comments

Though this algorithm requires the internet. Interestingly, using algorithm='sympy' gives AttributeError: 'NonElementaryIntegral' object has no attribute '_sage_'.

( 2015-03-11 16:06:55 +0200 )edit

Unfortunately, the mathematica_free algorithm will not work from within Sage Math Cloud with current connection settings.

( 2015-03-11 16:10:25 +0200 )edit

But the correct answer is a numerical value or exact expression pi^2/4. So, algorithm = 'mathematica_free' doesn't work.

( 2015-03-11 17:39:28 +0200 )edit

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Asked: 2015-03-11 14:33:19 +0200

Seen: 1,266 times

Last updated: Mar 11 '15