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Non-orthogonal eigenvectors with DSBGVX

PostPosted: Mon Nov 09, 2015 5:30 am
by bradders2421
I have a problem when calculating the eigenvectors of a 148x148 symmetric band matrix that two of the four eigenvectors calculated are clearly not orhtogonal. DSBGVX is being called with RANGE='I'. This occurs in version 3.4.2 of BLAS and LAPACK built with optimisations turned off in Visual Studio on Windows. When I set all small values (e.g. all values < machine precision * value of largest element) to zero, the problem goes away. Therefore, I suspect this is to do with some major loss of precision.

Do you think that this could be the same as bugs 56 and/or 126?

Many thanks