# calculating residue with maxima_methods

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?

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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))

more

( 2012-07-07 23:17:33 +0200 )edit

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.

more

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.

( 2012-07-24 07:18:18 +0200 )edit

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

( 2012-07-24 11:52:33 +0200 )edit