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[Lapack] Enquiry.

Dear J. J. Dongarra,

 

May I ask a favor from you, please? I have been trying to obtain the
eigenvalues and eigenvectors of a symmetric tridiagonal matrix using CLAPACK
rountines (dstegr_, dstevr_, dstevx_, dsterf_, dsyevr_ dsyevd_) on a Dell
Pentium 4 PC that operates in Vine Linux 3.1. The eigenvalues that I
obtained from all these routines are the same, that is, E1 = -536 meV, E2 =
57 meV, and E3 =185 meV. The correct values are approximately E1 = 30 meV,
E2 = 112 meV and E3 = 188 meV. I have checked the diagonal elements and sub-
and super diagonal elements that I passed to dstegr_, dstevr_, dstevx_, and
dsterf_ by constructing the symmetric tridiagonal matrix and solve for the
eigenvalues and eigenvectors using Igor Pro 4.01A. Correct eigenvalues and
eigenvectors were obtained using Igor Pro 4.01A that uses LAPACK routines.
Unfortunately, the LAPACK routines that Igor Pro 4.01A uses to calculate the
eigenvalues and eigenvectors of the matrix were not known. I have checked
the matrix passed to dsyevr_ dsyevd_() by using Igor Pro 4.01A to calculate
the eigenvalues and vectors of this matrix, and correct eigenvalues and
eigenvectors were obtained. I have also tried dgeevx_ but I got E1 = nan
meV, E2 = nan meV, and E3 = nan meV. The value of INFO passed back from
CLAPACK routines is 0 for all the above CLAPACK routines that I have tried.
May I have your valuable advice on how could I obtain the correct
eigenvalues and eigenvectors using CLAPACK on Linux, please? I have attached
the 400x400 matrix (i.e., C.dat), its diagonal elements (i.e., B.dat) and
sub-/super-diagonal elements (i.e., A.dat), source files as well as the
400x400 matrix (i.e., Matrix.dat) that Igor Pro 4.01A solves to this e-mail.
Thank you very much for your kind attention, and I look forward earnestly to
your valuable advice.

 

Yours sincerely,

Cheng

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