[Maxima-bugs] [ maxima-Bugs-3542438 ] wrong residue

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Bugs item #3542438, was opened at 2012-07-10 23:37
Message generated for change (Comment added) made by rtoy
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Category: Lisp Core - Complex
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Aleksas (aleksasd)
Assigned to: Nobody/Anonymous (nobody)
Summary: wrong residue

Initial Comment:
 Wrong:
(%i1) residue(1/(x^8+1),x,exp(%i*%pi/8));
(%o1) 0
 The correct result is: 
(%i2) exp(-(7*%i*%pi)/8)/8;
(%o2) %e^(-(7*%i*%pi)/8)/8
(%i3) rectform(%);
(%o3) cos((7*%pi)/8)/8-(%i*sin((7*%pi)/8))/8
(%i4) float(%), numer;
(%o4) -0.047835429045636*%i-0.11548494156391
 or
(%i5) -exp(%i*%pi/8)/8;
(%o5) -%e^((%i*%pi)/8)/8
(%i6) rectform(%);
(%o6) -(%i*sin(%pi/8))/8-cos(%pi/8)/8
(%i7) float(%), numer;
(%o7) -0.047835429045636*%i-0.11548494156391

build_info("5.27.0","2012-04-24 08:52:03","i686-pc-mingw32","GNU Common Lisp (GCL)","GCL 2.6.8")

Aleksas D

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>Comment By: Raymond Toy (rtoy)
Date: 2012-07-22 17:00

Message:
This appears to be a bug in the function coeff, called from resm1 in
src/residu.lisp.  AFAICT, the taylor series returns the correct value, but
coeff is unable to get the coefficient of 1/(x-p).

A workaround is the remove the call ($ratsimp ($rectform pole)).  This
fixes both this bug and bug 3541292, without causing a regression in bug
1504505.

But coeff should really be fixed to return the correct value.


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