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Re: Eigenvalues broken?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg102836] Re: [mg102827] Eigenvalues broken?
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Sat, 29 Aug 2009 06:30:24 -0400 (EDT)
  • References: <200907310952.FAA19221@smc.vnet.net> <h50sjj$6pl$1@smc.vnet.net> <200908280447.AAA29021@smc.vnet.net>

On Aug 28, 2009, at 12:47 AM, vadim.oganesyan at gmail.com wrote:

> I have been doing full diagonalization of sparse symmetric real
> matrices (Hamiltonians) of different sizes and just noticed that
> Eigenvalues (and Eigensystem) break once the matrices are 256by256
> (maybe smaller, but that's where i first saw it).
>
> i first noticed the problem when checking the quality of the solutions
> by comparing eigenvalues with expectation of the matrix in each of
> eigenvectors.
>
> even more dramatically, simply rerunning Eigenvalues twice on the same
> matrix produces somewhat different results!!!
>
> If I chose to get only few eigenvales (thus forcing it to use Arnoldi
> method) the problem goes away.
>
> I was recently told that the version of Lapack used by Mathemica was
> recompiled by people at Wolfram for added functionality -- did they
> break it too?
> My trusty C++ code has no problems with these matrices....
>
> thoughts? suggestions?

What platform are you using?  I've had problems with the numeric  
linear algebra routines on OS X, the same code seems to work on Windows.

Regards,

Sseziwa


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