calculating residue with maxima_methods

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The following used to work around six months ago on sagenb.org:

var('x')
var('t')
( x/((4*x - 1)*(t^2 - t + x)) ).maxima_methods().residue(t,(1-sqrt(1-4*x))/2)

but now it returns zero which is incorrect. Can anybody help me get the correct answer again?

asked Jul 07 '12

Stefán Ingi gravatar image Stefán Ingi
13 3

2 Answers:

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sage: from sympy import Symbol, residue
sage:  x = Symbol("x")
sage:  t = Symbol("t")
sage: residue(x/((4*x - 1)*(t^2 - t + x)),t,(1-sqrt(1-4*x))/2)
-x/((-4*x + 1)**(1/2)*(4*x - 1))
link

posted Jul 07 '12

achrzesz gravatar image achrzesz
1741 5 18 39

I didn't know Sympy had this... see also http://trac.sagemath.org/sage_trac/ticket/11210

kcrisman (Jul 07 '12)
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I get this in a very old version of Sage's Maxima, the current Sage Maxima, and the most recent one I have.

Maxima 5.27.0 http://maxima.sourceforge.net
using Lisp SBCL 1.0.24
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1)  residue(( x/((4*x - 1)*(t^2 - t + x)) ),t,(1-sqrt(1-4*x))/2);
(%o1)                                  0

What/when was the answer you got before? I can't get this to do anything else in any version of Sage, either, not just the Maxima in it.

This is now Maxima artifact 3541292; I've also put it at the relevant Sage ticket.

link

posted Jul 07 '12

kcrisman gravatar image kcrisman
7827 20 78 170

updated Jul 07 '12

I was reexamining my old code and found the culprit. When it worked before I had run "assume(x<1/8)". That makes maxima give the same answer as sympy. Sorry for the trouble, but at least I learned something about sympy.

Stefán Ingi (Jul 24 '12)

Hmm, that's interesting. I'll add that to the bug report.

kcrisman (Jul 24 '12)

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Asked: Jul 07 '12

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Last updated: Jul 07 '12

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