sstev(3S)

NAME
     SSTEV - compute all eigenvalues and, optionally, eigenvectors of a real
     symmetric tridiagonal matrix A

SYNOPSIS
     SUBROUTINE SSTEV( JOBZ, N, D, E, Z, LDZ, WORK, INFO )

         CHARACTER     JOBZ

         INTEGER       INFO, LDZ, N

         REAL          D( * ), E( * ), WORK( * ), Z( LDZ, * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     SSTEV computes all eigenvalues and, optionally, eigenvectors of a real
     symmetric tridiagonal matrix A.

ARGUMENTS
     JOBZ    (input) CHARACTER*1
             = 'N':  Compute eigenvalues only;
             = 'V':  Compute eigenvalues and eigenvectors.

     N       (input) INTEGER
             The order of the matrix.  N >= 0.

     D       (input/output) REAL array, dimension (N)
             On entry, the n diagonal elements of the tridiagonal matrix A.
             On exit, if INFO = 0, the eigenvalues in ascending order.

     E       (input/output) REAL array, dimension (N)
             On entry, the (n-1) subdiagonal elements of the tridiagonal
             matrix A, stored in elements 1 to N-1 of E; E(N) need not be set,
             but is used by the routine.  On exit, the contents of E are
             destroyed.

     Z       (output) REAL array, dimension (LDZ, 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 D(i).  If JOBZ = 'N', then Z is
             not referenced.

     LDZ     (input) INTEGER
             The leading dimension of the array Z.  LDZ >= 1, and if JOBZ =
             'V', LDZ >= max(1,N).

     WORK    (workspace) REAL array, dimension (max(1,2*N-2))
             If JOBZ = 'N', WORK is not referenced.

     INFO    (output) INTEGER
             = 0:  successful exit
             < 0:  if INFO = -i, the i-th argument had an illegal value
             > 0:  if INFO = i, the algorithm failed to converge; i off-
             diagonal elements of E did not converge to zero.

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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