[Octave-bug-tracker] [bug #42097] 64bit Slackware, eig returning incorrect results

[Russell Carden]

Follow-up Comment #28, bug #42097 (project octave):

So both the test program and octave produce the same results up
to line 466 of dhseqr.f.
466  CALL DLAHQR( WANTT, WANTZ, N, ILO, IHI, H, LDH, WR, WI, ILO,
467          $                   IHI, Z, LDZ, INFO )
At this point I am able to step into DLAHQR in my test program, but in gdb for
octave I step right over this function call.  After this function call the
results from octave are incorrect.  
After some googling, I found that I should tell gdb
set step-mode on
I then found that that there is a dlahqr_ that is used in arpack
and this is the dlahqr_ that octave is calling.
Note, the version of arpack that I installed is arpack-ng.  Supposedly
arpack-ng is actively maintained while the regular arpack is not.  When I saw
this, I removed arpack-ng and installed the regular arpack, and now I have the
correct results.
Apparently the regular arpack build script has an important flag/option that
arpack-ng is missing.


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