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A Clone of Maxima's repo
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eigenvectors() extremely slow to output an unusable answer #2276

Open rtoy opened 4 months ago

rtoy commented 4 months ago

Imported from SourceForge on 2024-07-05 22:40:24 Created by charpent on 2016-11-13 19:30:47 Original: https://sourceforge.net/p/maxima/bugs/3243

Not unrelated to bugs:#3239.

build_info(version="5.38.1",timestamp="2016-11-01 13:12:23",host=
"x86_64-pc-linux-gnu",lisp_name="GNU Common Lisp (GCL)",lisp_version="GCL 2.6.12")

Given :

Mx:matrix([1,0,0],[0,cos(theta),-sin(theta)],[0,sin(theta),cos(theta)]);
My:matrix([cos(phi),0,-sin(phi)],[0,1,0],[sin(phi),0,cos(phi)]);

The following :

 eigenvectors(My.Mx);
  1. Needs about 10 minutes, to
  2. output tens of pages of trig giberrish.

According to a bit of research in Sage's Maxima (5.35.1, ECL), this is not the same as a recently fixed bug in eigenvalues(). See bugs:#3239's discussion.

rtoy commented 4 months ago

Imported from SourceForge on 2024-07-05 22:40:25 Created by robert_dodier on 2022-11-03 16:42:18 Original: https://sourceforge.net/p/maxima/bugs/3243/#dc33

rtoy commented 4 months ago

Imported from SourceForge on 2024-07-05 22:40:28 Created by macrakis on 2022-11-03 17:24:47 Original: https://sourceforge.net/p/maxima/bugs/3243/#39f8

I also got a result in 2.5 secs (Maxima 5.45.1 SBCL 2.0.0).

Is there any reason to believe that the result is incorrect? In general, the eigenvalues of a symbolic 3x3 matrix involve the solutions of a cubic polynomial, which are usually messy.