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DSTEV(3F)							     DSTEV(3F)


NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

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

	 CHARACTER     JOBZ

	 INTEGER       INFO, LDZ, N

	 DOUBLE	       PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )

PURPOSE    [Toc]    [Back]

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

ARGUMENTS    [Toc]    [Back]

     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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE	PRECISION 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



									Page 1






DSTEV(3F)							     DSTEV(3F)



	     > 0:  if INFO = i,	the algorithm failed to	converge; i offdiagonal
 elements of E did	not converge to	zero.
DSTEV(3F)							     DSTEV(3F)


NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

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

	 CHARACTER     JOBZ

	 INTEGER       INFO, LDZ, N

	 DOUBLE	       PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )

PURPOSE    [Toc]    [Back]

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

ARGUMENTS    [Toc]    [Back]

     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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE	PRECISION 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



									Page 1






DSTEV(3F)							     DSTEV(3F)



	     > 0:  if INFO = i,	the algorithm failed to	converge; i offdiagonal
 elements of E did	not converge to	zero.


									PPPPaaaaggggeeee 2222
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