Visible to Intel only — GUID: GUID-F7CD8DF8-E804-4EF7-AE12-444F588C9B76
Visible to Intel only — GUID: GUID-F7CD8DF8-E804-4EF7-AE12-444F588C9B76
?stev
Computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix.
Syntax
call sstev(jobz, n, d, e, z, ldz, work, info)
call dstev(jobz, n, d, e, z, ldz, work, info)
call stev(d, e [,z] [,info])
Include Files
- mkl.fi, lapack.f90
Description
The routine computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A.
Input Parameters
- jobz
-
CHARACTER*1. Must be 'N' or 'V'.
If jobz = 'N', then only eigenvalues are computed.
If jobz = 'V', then eigenvalues and eigenvectors are computed.
- n
-
INTEGER. The order of the matrix A (n≥ 0).
- d, e, work
-
REAL for sstev
DOUBLE PRECISION for dstev.
Arrays:
Array d(*) contains the n diagonal elements of the tridiagonal matrix A.
The size of d must be at least max(1, n).
Array e(*) contains the n-1 subdiagonal elements of the tridiagonal matrix A.
The size of e must be at least max(1, n). The n-th element of this array is used as workspace.
work(*) is a workspace array.
The dimension of work must be at least max(1, 2n-2).
If jobz = 'N', work is not referenced.
- ldz
-
INTEGER. The leading dimension of the output array z; ldz≥ 1. If jobz = 'V' then ldz≥ max(1, n).
Output Parameters
- d
-
On exit, if info = 0, contains the eigenvalues of the matrix A in ascending order.
- z
-
REAL for sstev
DOUBLE PRECISION for dstev
Array, size (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 the eigenvalue returned in d(i).
If job = 'N', then z is not referenced.
- e
-
On exit, this array is overwritten with intermediate results.
- 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 elements of e 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 stev interface are the following:
- d
-
Holds the vector of length n.
- e
-
Holds the vector of length n.
- z
-
Holds the matrix Z of size (n, n).
- jobz
-
Restored based on the presence of the argument z as follows:
jobz = 'V', if z is present,
jobz = 'N', if z is omitted.