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RedHat 9 (Linux i386) - man page for sstevd (redhat section l)

SSTEVD(l)					)					SSTEVD(l)

NAME
       SSTEVD  - compute all eigenvalues and, optionally, eigenvectors of a real symmetric tridi-
       agonal matrix

SYNOPSIS
       SUBROUTINE SSTEVD( JOBZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK, LIWORK, INFO )

	   CHARACTER	  JOBZ

	   INTEGER	  INFO, LDZ, LIWORK, LWORK, N

	   INTEGER	  IWORK( * )

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

PURPOSE
       SSTEVD computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiag-
       onal matrix. If eigenvectors are desired, it uses a divide and conquer algorithm.

       The  divide  and conquer algorithm makes very mild assumptions about floating point arith-
       metic. It will work on machines with a guard digit in add/subtract,  or	on  those  binary
       machines  without guard digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or
       Cray-2. It could conceivably fail on hexadecimal or decimal machines without guard digits,
       but we know of none.

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/output) REAL array,
	       dimension (LWORK) On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

       LWORK   (input) INTEGER
	       The  dimension  of the array WORK.  If JOBZ  = 'N' or N <= 1 then LWORK must be at
	       least 1.  If JOBZ  = 'V' and N > 1 then LWORK must be at least ( 1 + 4*N + N**2 ).

	       If LWORK = -1, then a workspace query is assumed; the routine only calculates  the
	       optimal	size of the WORK array, returns this value as the first entry of the WORK
	       array, and no error message related to LWORK is issued by XERBLA.

       IWORK   (workspace/output) INTEGER array, dimension (LIWORK)
	       On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.

       LIWORK  (input) INTEGER
	       The dimension of the array IWORK.  If JOBZ  = 'N' or N <= 1 then LIWORK must be at
	       least 1.  If JOBZ  = 'V' and N > 1 then LIWORK must be at least 3+5*N.

	       If LIWORK = -1, then a workspace query is assumed; the routine only calculates the
	       optimal size of the IWORK array, returns this value as  the  first  entry  of  the
	       IWORK array, and no error message related to LIWORK is issued by XERBLA.

       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.

LAPACK version 3.0			   15 June 2000 				SSTEVD(l)


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