Eigenvalues broken?
- To: mathgroup at smc.vnet.net
- Subject: [mg102827] Eigenvalues broken?
- From: "vadim.oganesyan at gmail.com" <vadim.oganesyan at gmail.com>
- Date: Fri, 28 Aug 2009 00:47:04 -0400 (EDT)
- References: <200907310952.FAA19221@smc.vnet.net> <h50sjj$6pl$1@smc.vnet.net>
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? thanks! PS i can send the matrix in a file to anybody willing to look into this
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