Visible to Intel only — GUID: GUID-DF5ABE75-6E20-4B5A-94A8-BBF2D28C7B74
Visible to Intel only — GUID: GUID-DF5ABE75-6E20-4B5A-94A8-BBF2D28C7B74
?spev
Computes all eigenvalues and, optionally, eigenvectors of a real symmetric matrix in packed storage.
Syntax
call sspev(jobz, uplo, n, ap, w, z, ldz, work, info)
call dspev(jobz, uplo, n, ap, w, z, ldz, work, info)
call spev(ap, w [,uplo] [,z] [,info])
Include Files
- mkl.fi, lapack.f90
Description
The routine computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage.
Input Parameters
- jobz
-
CHARACTER*1. Must be 'N' or 'V'.
If job = 'N', then only eigenvalues are computed.
If job = 'V', then eigenvalues and eigenvectors are computed.
- uplo
-
CHARACTER*1. Must be 'U' or 'L'.
If uplo = 'U', ap stores the packed upper triangular part of A.
If uplo = 'L', ap stores the packed lower triangular part of A.
- n
-
INTEGER. The order of the matrix A (n≥ 0).
- ap, work
-
REAL for sspev
DOUBLE PRECISION for dspev
Arrays:
Array ap(*) contains the packed upper or lower triangle of symmetric matrix A, as specified by uplo.
The size of ap must be at least max(1, n*(n+1)/2).
work(*) is a workspace array, size at least max(1, 3n).
- ldz
-
INTEGER. The leading dimension of the output array z. Constraints:
if jobz = 'N', then ldz≥ 1;
if jobz = 'V', then ldz≥ max(1, n).
Output Parameters
- w, z
-
REAL for sspev
DOUBLE PRECISION for dspev
Arrays:
w(*), size at least max(1, n).
If info = 0, w contains the eigenvalues of the matrix A in ascending order.
z(ldz,*). The second dimension of z must be at least max(1, n).
If jobz = 'V', then if info = 0, z contains the orthonormal eigenvectors of the matrix A, with the i-th column of z holding the eigenvector associated with w(i).
If jobz = 'N', then z is not referenced.
- ap
-
On exit, this array is overwritten by the values generated during the reduction to tridiagonal form. The elements of the diagonal and the off-diagonal of the tridiagonal matrix overwrite the corresponding elements of A.
- info
-
INTEGER.
If info = 0, the execution is successful.
If info = -i, the i-th parameter had an illegal value.
If info = i, then the algorithm failed to converge; i indicates the number of elements of an intermediate tridiagonal form which did not converge to zero.
LAPACK 95 Interface Notes
Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or restorable arguments, see LAPACK 95 Interface Conventions.
Specific details for the routine spev interface are the following:
- ap
-
Holds the array A of size (n*(n+1)/2).
- w
-
Holds the vector with the number of elements n.
- z
-
Holds the matrix Z of size (n, n).
- uplo
-
Must be 'U' or 'L'. The default value is 'U'.
- jobz
-
Restored based on the presence of the argument z as follows: jobz = 'V', if z is present, jobz = 'N', if z is omitted.