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

**References**:**Eigenvalues broken?***From:*"vadim.oganesyan@gmail.com" <vadim.oganesyan@gmail.com>