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[Lapack] dsyev and dsyevd

Dear Gabriel,

thank you for letting me know.
Good luck with your code!

Bedrich


On Wed, Feb 16, 2011 at 8:27 AM, GG Balint-Kurti
<Gabriel.Balint-Kurti@Domain.Removed> wrote:
Dear Bedrich,

Thank you again for your response. I now think that my problems are of my
own making and are not caused by any failure of the dsyev routine.

Again -- thank you for your trouble.

Gabriel Balint-Kurti

--On 15 February 2011 09:17 -0700 Bedrich Sousedik
<bedrich.sousedik@Domain.Removed> wrote:

Dear Gabriel,

this indeed seems unexpected.
Can you please send me your sample (8x8) matrix and a piece of your code
(small extract that would reproduce the problem you are running into).

Thank you,

Bedrich


On Mon, Feb 14, 2011 at 4:07 PM, GG Balint-Kurti
<Gabriel.Balint-Kurti@Domain.Removed> wrote:

Dear LAPACK,

I have been using subroutines dsyev and dsyevd to compute the
eigenvectors and eigenvalues of a symmetric 8x8 matrix. the matrix
formed by these eigenvectors should form a unitary matrix and therefore
be the basis of a unitary transformation. When I test the unitariy of
the resulting matrix I find that it is quite inaccurate. In particular I
find that the scalar product of two of the eigenvectors is 3.8D-5. this
is far less accurate than I would like. As I need to perform at least
40,000 unitary transformations in my dynamical calculations such a large
error allows a large build-up of errors and renders my calculations
invalid.

All my variables are double precision. Can you advise as to how I can
improve the accuracy of my eigenvectors.

Gabriel Balint-Kurti
Professor of Theoretical Chemistry

----------------------
Gabriel Balint-Kurti
Centre for Computational Chemistry
School of Chemistry
University of Bristol
Bristol, BS8 1TS
Tel: +44 117 928 7662
fax: +44 117 925 1295
Gabriel.Balint-Kurti@Domain.Removed
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----------------------
Gabriel Balint-Kurti
Centre for Computational Chemistry
School of Chemistry
University of Bristol
Bristol, BS8 1TS
Tel: +44 117 928 7662
fax: +44 117 925 1295
Gabriel.Balint-Kurti@Domain.Removed


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