ASKSAGE: Sage Q&A Forum - RSS feedhttps://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Wed, 20 Jan 2021 21:48:55 +0100Possible inconsistency in symbolic limitshttps://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/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?Wed, 20 Jan 2021 02:58:40 +0100https://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/Answer by FrédéricC for <p>I was trying to manipulate some symbolic expressions and got an unexpected error.
Here is a minimal example,</p>
<pre><code>u=integrate(x**3/(exp(x)-1),(x,0,oo))
</code></pre>
<p>The expression is quite messy, but the result is known. When I try to use any simplification routine, like</p>
<pre><code>u.simplify()
</code></pre>
<p>sage displays the error message</p>
<pre><code>RuntimeError: ECL says: Error executing code in Maxima: limit: direction must be either 'plus' or 'minus'; found: _SAGE_VAR_minus
</code></pre>
<p>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?</p>
https://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/?answer=55372#post-id-55372Looks 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^4Wed, 20 Jan 2021 09:07:45 +0100https://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/?answer=55372#post-id-55372Comment by FrédéricC for <p>Looks like a bug indeed. You may use instead </p>
<pre><code>sage: u=integrate(x**3/(exp(x)-1),(x,0,oo),algorithm='giac');u
1/15*pi^4
</code></pre>
https://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/?comment=55373#post-id-55373Smaller 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()Wed, 20 Jan 2021 10:26:07 +0100https://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/?comment=55373#post-id-55373Comment by cav_rt for <p>Looks like a bug indeed. You may use instead </p>
<pre><code>sage: u=integrate(x**3/(exp(x)-1),(x,0,oo),algorithm='giac');u
1/15*pi^4
</code></pre>
https://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/?comment=55400#post-id-55400Thank you!Wed, 20 Jan 2021 21:48:55 +0100https://ask.sagemath.org/question/55370/possible-inconsistency-in-symbolic-limits/?comment=55400#post-id-55400