\brief \b ESMF_DSTEQR \htmlonly Download ESMF_DSTEQR + dependencies [TGZ] [ZIP] [TXT] \endhtmlonly \par Purpose:
\verbatim
ESMF_DSTEQR computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. The eigenvectors of a full or band symmetric matrix can also be found if ESMF_DSYTRD or DSPTRD or DSBTRD has been used to reduce this matrix to tridiagonal form. \endverbatim \param[in] COMPZ \verbatim COMPZ is CHARACTER*1 = ‘N’: Compute eigenvalues only. = ‘V’: Compute eigenvalues and eigenvectors of the original symmetric matrix. On entry, Z must contain the orthogonal matrix used to reduce the original matrix to tridiagonal form. = ‘I’: Compute eigenvalues and eigenvectors of the tridiagonal matrix. Z is initialized to the identity matrix. \endverbatim
\param[in] N \verbatim N is INTEGER The order of the matrix. N >= 0. \endverbatim
\param[in,out] D \verbatim D is DOUBLE PRECISION array, dimension (N) On entry, the diagonal elements of the tridiagonal matrix. On exit, if INFO = 0, the eigenvalues in ascending order. \endverbatim
\param[in,out] E \verbatim E is DOUBLE PRECISION array, dimension (N-1) On entry, the (n-1) subdiagonal elements of the tridiagonal matrix. On exit, E has been destroyed. \endverbatim
\param[in,out] Z \verbatim Z is DOUBLE PRECISION array, dimension (LDZ, N) On entry, if COMPZ = ‘V’, then Z contains the orthogonal matrix used in the reduction to tridiagonal form. On exit, if INFO = 0, then if COMPZ = ‘V’, Z contains the orthonormal eigenvectors of the original symmetric matrix, and if COMPZ = ‘I’, Z contains the orthonormal eigenvectors of the symmetric tridiagonal matrix. If COMPZ = ‘N’, then Z is not referenced. \endverbatim
\param[in] LDZ \verbatim LDZ is INTEGER The leading dimension of the array Z. LDZ >= 1, and if eigenvectors are desired, then LDZ >= max(1,N). \endverbatim
\param[out] WORK \verbatim WORK is DOUBLE PRECISION array, dimension (max(1,2*N-2)) If COMPZ = ‘N’, then WORK is not referenced. \endverbatim
\param[out] INFO \verbatim INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value > 0: the algorithm has failed to find all the eigenvalues in a total of 30*N iterations; if INFO = i, then i elements of E have not converged to zero; on exit, D and E contain the elements of a symmetric tridiagonal matrix which is orthogonally similar to the original matrix. \endverbatim \author Univ. of Tennessee \author Univ. of California Berkeley \author Univ. of Colorado Denver \author NAG Ltd. \date December 2016 \ingroup auxOTHERcomputational
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| character(len=1) | :: | COMPZ | ||||
| integer | :: | N | ||||
| double precision | :: | D(*) | ||||
| double precision | :: | E(*) | ||||
| double precision | :: | Z(LDZ,*) | ||||
| integer | :: | LDZ | ||||
| double precision | :: | WORK(*) | ||||
| integer | :: | INFO |