Visible to Intel only — GUID: GUID-43194A76-1612-4587-B31C-E5B16041A46D
Visible to Intel only — GUID: GUID-43194A76-1612-4587-B31C-E5B16041A46D
?steqr2
Computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method.
Syntax
void ssteqr2 (char *compz , MKL_INT *n , float *d , float *e , float *z , MKL_INT *ldz , MKL_INT *nr , float *work , MKL_INT *info );
void dsteqr2 (char *compz , MKL_INT *n , double *d , double *e , double *z , MKL_INT *ldz , MKL_INT *nr , double *work , MKL_INT *info );
Include Files
- mkl_scalapack.h
Description
The ?steqr2function is a modified version of LAPACK function ?steqr. The ?steqr2function computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. ?steqr2 is modified from ?steqr to allow each ScaLAPACK process running ?steqr2 to perform updates on a distributed matrix Q. Proper usage of ?steqr2 can be gleaned from examination of ScaLAPACK function p?syev.
Input Parameters
- compz
-
Must be 'N' or 'I'.
If compz = 'N', the function computes eigenvalues only. If compz = 'I', the function computes the eigenvalues and eigenvectors of the tridiagonal matrix T.
z must be initialized to the identity matrix by p?laset or ?laset prior to entering this function.
- n
-
The order of the matrix T(n ≥ 0).
- d, e, work
-
Arrays:
d contains the diagonal elements of T. The size of d must be at least max(1, n).
e contains the (n-1) subdiagonal elements of T. The size of e must be at least max(1, n-1).
work is a workspace array. The size of work is max(1, 2*n-2). If compz = 'N', then work is not referenced.
- z
-
(local)
Array of global size n* n and of local size ldz* nr.
If compz = 'V', then z contains the orthogonal matrix used in the reduction to tridiagonal form.
- ldz
-
The leading dimension of the array z. Constraints:
ldz ≥ 1,
ldz ≥ max(1, n), if eigenvectors are desired.
- nr
-
nr = max(1, numroc(n, nb, myprow, 0, nprocs)).
If compz = 'N', then nr is not referenced.
Output Parameters
- d
-
On exit, the eigenvalues in ascending order, if info = 0.
See also info.
- e
-
On exit, e has been destroyed.
- z
-
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.
- info
-
info = 0, the exit is successful.
info < 0: if info = -i, the i-th had an illegal value.
info > 0: the algorithm has failed to find all the eigenvalues in a total of 30n 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.