ASKSAGE: Sage Q&A Forum - Individual question feedhttp://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Thu, 15 Dec 2016 06:10:27 -0600What is _SAGE_VAR_(0)?http://ask.sagemath.org/question/36025/what-is-_sage_var_0/Using SageMath 7.4, I do the following:
sage: var('u R omega')
sage: hs = (1+u^R).series(u==omega, 2); hs
(omega^R + 1) + (R*omega^R/omega)*(-omega + u) + Order((omega - u)^2)
sage: hs.subs({omega^R: -1}).simplify()
R*(omega - u)/omega + Order((omega - u)^2) + _SAGE_VAR_(0)
I am wondering what `_SAGE_VAR_(0)` shall be and how to get rid of it.
Thu, 15 Dec 2016 04:23:52 -0600http://ask.sagemath.org/question/36025/what-is-_sage_var_0/Answer by kcrisman for <p>Using SageMath 7.4, I do the following:</p>
<pre><code>sage: var('u R omega')
sage: hs = (1+u^R).series(u==omega, 2); hs
(omega^R + 1) + (R*omega^R/omega)*(-omega + u) + Order((omega - u)^2)
sage: hs.subs({omega^R: -1}).simplify()
R*(omega - u)/omega + Order((omega - u)^2) + _SAGE_VAR_(0)
</code></pre>
<p>I am wondering what <code>_SAGE_VAR_(0)</code> shall be and how to get rid of it.</p>
http://ask.sagemath.org/question/36025/what-is-_sage_var_0/?answer=36026#post-id-36026That is a leftover from Maxima's translation back to Sage. Somehow it didn't get translated. Looking at the precise expression `hs`, I suspect probably `_SAGE_VAR_(0)` is what came out of `omega^R + 1`, which then becomes zero - but a symbolic zero. So we are probably missing a translation in series (or in general) when a symbolic zero is brought back from Maxima. I don't have a solution for that but those with time in the know should be able to get it from that.
Edit: This is definitely known and apparently even a fix is available, we need someone to review and test it.
> See https://trac.sagemath.org/ticket/20846 and https://trac.sagemath.org/ticket/17400
which needs review.Thu, 15 Dec 2016 06:10:27 -0600http://ask.sagemath.org/question/36025/what-is-_sage_var_0/?answer=36026#post-id-36026