redhat man page for slaed0

SLAED0(l)								 )								 SLAED0(l)

NAME
       SLAED0 - compute all eigenvalues and corresponding eigenvectors of a symmetric tridiagonal matrix using the divide and conquer method

SYNOPSIS
       SUBROUTINE SLAED0( ICOMPQ, QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, WORK, IWORK, INFO )

	   INTEGER	  ICOMPQ, INFO, LDQ, LDQS, N, QSIZ

	   INTEGER	  IWORK( * )

	   REAL 	  D( * ), E( * ), Q( LDQ, * ), QSTORE( LDQS, * ), WORK( * )

PURPOSE
       SLAED0 computes all eigenvalues and corresponding eigenvectors of a symmetric tridiagonal matrix using the divide and conquer method.

ARGUMENTS
       ICOMPQ  (input) INTEGER
	       = 0:  Compute eigenvalues only.
	       =  1:  Compute eigenvectors of original dense symmetric matrix also.  On entry, Q contains the orthogonal matrix used to reduce the
	       original matrix to tridiagonal form.  = 2:  Compute eigenvalues and eigenvectors of tridiagonal matrix.

       QSIZ   (input) INTEGER
	      The dimension of the orthogonal matrix used to reduce the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1.

       N      (input) INTEGER
	      The dimension of the symmetric tridiagonal matrix.  N >= 0.

       D      (input/output) REAL array, dimension (N)
	      On entry, the main diagonal of the tridiagonal matrix.  On exit, its eigenvalues.

       E      (input) REAL array, dimension (N-1)
	      The off-diagonal elements of the tridiagonal matrix.  On exit, E has been destroyed.

       Q      (input/output) REAL array, dimension (LDQ, N)
	      On entry, Q must contain an N-by-N orthogonal matrix.  If ICOMPQ = 0    Q is not referenced.  If ICOMPQ = 1    On entry, Q is a sub-
	      set  of  the  columns of the orthogonal matrix used to reduce the full matrix to tridiagonal form corresponding to the subset of the
	      full matrix which is being decomposed at this time.  If ICOMPQ = 2    On entry, Q will be the identity matrix.  On exit, Q  contains
	      the eigenvectors of the tridiagonal matrix.

       LDQ    (input) INTEGER
	      The leading dimension of the array Q.  If eigenvectors are desired, then	LDQ >= max(1,N).  In any case,	LDQ >= 1.

	      QSTORE  (workspace)  REAL array, dimension (LDQS, N) Referenced only when ICOMPQ = 1.  Used to store parts of the eigenvector matrix
	      when the updating matrix multiplies take place.

       LDQS   (input) INTEGER
	      The leading dimension of the array QSTORE.  If ICOMPQ = 1, then  LDQS >= max(1,N).  In any case,	LDQS >= 1.

       WORK   (workspace) REAL array,
	      If ICOMPQ = 0 or 1, the dimension of WORK must be at least 1 + 3*N + 2*N*lg N + 2*N**2 ( lg( N ) = smallest integer k such that  2^k
	      >= N ) If ICOMPQ = 2, the dimension of WORK must be at least 4*N + N**2.

       IWORK  (workspace) INTEGER array,
	      If ICOMPQ = 0 or 1, the dimension of IWORK must be at least 6 + 6*N + 5*N*lg N.  ( lg( N ) = smallest integer k such that 2^k >= N )
	      If ICOMPQ = 2, the dimension of IWORK must be at least 3 + 5*N.

       INFO   (output) INTEGER
	      = 0:  successful exit.
	      < 0:  if INFO = -i, the i-th argument had an illegal value.
	      > 0:  The algorithm failed to compute an eigenvalue while working on the submatrix lying in  rows  and  columns  INFO/(N+1)  through
	      mod(INFO,N+1).

FURTHER DETAILS
       Based on contributions by
	  Jeff Rutter, Computer Science Division, University of California
	  at Berkeley, USA

LAPACK version 3.0						   15 June 2000 							 SLAED0(l)