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Possible inconsistency in symbolic limits

asked 2021-01-20 02:58:40 +0200

cav_rt gravatar image

updated 2021-01-20 14:50:11 +0200

slelievre gravatar image

I was trying to manipulate some symbolic expressions and got an unexpected error. Here is a minimal example,

u=integrate(x**3/(exp(x)-1),(x,0,oo))

The expression is quite messy, but the result is known. When I try to use any simplification routine, like

u.simplify()

sage displays the error message

RuntimeError: ECL says: Error executing code in Maxima: limit: direction must be either 'plus' or 'minus'; found: _SAGE_VAR_minus

As far I understood, the expression is defining lateral limits by symbolic variables, while maxima handle such limits as strings. If it is the case there is an internal conflict here. Is it the case?

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answered 2021-01-20 09:07:45 +0200

FrédéricC gravatar image

Looks like a bug indeed. You may use instead

sage: u=integrate(x**3/(exp(x)-1),(x,0,oo),algorithm='giac');u                  
1/15*pi^4
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Comments

Smaller display of the same bug:

sage: maxima('limit(polylog(4,e^x),x,+Infinity,minus)').sage()                  
limit(polylog(4, _e^x), x, +Infinity, minus)
sage: _.simplify()
FrédéricC gravatar imageFrédéricC ( 2021-01-20 10:26:07 +0200 )edit

Thank you!

cav_rt gravatar imagecav_rt ( 2021-01-20 21:48:55 +0200 )edit

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Asked: 2021-01-20 02:58:40 +0200

Seen: 48 times

Last updated: Jan 20