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SSTEDC(3F)							    SSTEDC(3F)


NAME    [Toc]    [Back]

     SSTEDC - compute all eigenvalues and, optionally, eigenvectors of a
     symmetric tridiagonal matrix using	the divide and conquer method

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	SSTEDC(	COMPZ, N, D, E,	Z, LDZ,	WORK, LWORK, IWORK, LIWORK,
			INFO )

	 CHARACTER	COMPZ

	 INTEGER	INFO, LDZ, LIWORK, LWORK, N

	 INTEGER	IWORK( * )

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

PURPOSE    [Toc]    [Back]

     SSTEDC computes all eigenvalues and, optionally, eigenvectors of a
     symmetric tridiagonal matrix using	the divide and conquer method.	The
     eigenvectors of a full or band real symmetric matrix can also be found if
     SSYTRD or SSPTRD or SSBTRD	has been used to reduce	this matrix to
     tridiagonal form.

     This code makes very mild assumptions about floating point	arithmetic. 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.  See	SLAED3 for details.

ARGUMENTS    [Toc]    [Back]

     COMPZ   (input) CHARACTER*1
	     = 'N':  Compute eigenvalues only.
	     = 'I':  Compute eigenvectors of tridiagonal matrix	also.
	     = 'V':  Compute eigenvectors of original dense symmetric matrix
	     also.  On entry, Z	contains the orthogonal	matrix used to reduce
	     the original matrix to tridiagonal	form.

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

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

     E	     (input/output) REAL array,	dimension (N-1)
	     On	entry, the subdiagonal elements	of the tridiagonal matrix.  On
	     exit, E has been destroyed.






									Page 1






SSTEDC(3F)							    SSTEDC(3F)



     Z	     (input/output) REAL array,	dimension (LDZ,N)
	     On	entry, if COMPZ	= 'V', then Z contains the orthogonal matrix
	     used in the reduction to tridiagonal form.	 On exit, if INFO = 0,
	     then if COMPZ = 'V', Z contains the orthonormal eigenvectors of
	     the original symmetric matrix, and	if COMPZ = 'I',	Z contains the
	     orthonormal eigenvectors of the symmetric tridiagonal matrix.  If
	     COMPZ = 'N', then Z is not	referenced.

     LDZ     (input) INTEGER
	     The leading dimension of the array	Z.  LDZ	>= 1.  If eigenvectors
	     are desired, then LDZ >= max(1,N).

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

     LWORK   (input) INTEGER
	     The dimension of the array	WORK.  If COMPZ	= 'N' or N <= 1	then
	     LWORK must	be at least 1.	If COMPZ = 'V' and N > 1 then LWORK
	     must be at	least (	1 + 3*N	+ 2*N*lg N + 3*N**2 ), where lg( N ) =
	     smallest integer k	such that 2**k >= N.  If COMPZ = 'I' and N > 1
	     then LWORK	must be	at least ( 1 + 3*N + 2*N*lg N +	2*N**2 ).

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

     LIWORK  (input) INTEGER
	     The dimension of the array	IWORK.	If COMPZ = 'N' or N <= 1 then
	     LIWORK must be at least 1.	 If COMPZ = 'V'	and N >	1 then LIWORK
	     must be at	least (	6 + 6*N	+ 5*N*lg N ).  If COMPZ	= 'I' and N >
	     1 then LIWORK must	be at least ( 2	+ 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).
SSTEDC(3F)							    SSTEDC(3F)


NAME    [Toc]    [Back]

     SSTEDC - compute all eigenvalues and, optionally, eigenvectors of a
     symmetric tridiagonal matrix using	the divide and conquer method

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	SSTEDC(	COMPZ, N, D, E,	Z, LDZ,	WORK, LWORK, IWORK, LIWORK,
			INFO )

	 CHARACTER	COMPZ

	 INTEGER	INFO, LDZ, LIWORK, LWORK, N

	 INTEGER	IWORK( * )

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

PURPOSE    [Toc]    [Back]

     SSTEDC computes all eigenvalues and, optionally, eigenvectors of a
     symmetric tridiagonal matrix using	the divide and conquer method.	The
     eigenvectors of a full or band real symmetric matrix can also be found if
     SSYTRD or SSPTRD or SSBTRD	has been used to reduce	this matrix to
     tridiagonal form.

     This code makes very mild assumptions about floating point	arithmetic. 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.  See	SLAED3 for details.

ARGUMENTS    [Toc]    [Back]

     COMPZ   (input) CHARACTER*1
	     = 'N':  Compute eigenvalues only.
	     = 'I':  Compute eigenvectors of tridiagonal matrix	also.
	     = 'V':  Compute eigenvectors of original dense symmetric matrix
	     also.  On entry, Z	contains the orthogonal	matrix used to reduce
	     the original matrix to tridiagonal	form.

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

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

     E	     (input/output) REAL array,	dimension (N-1)
	     On	entry, the subdiagonal elements	of the tridiagonal matrix.  On
	     exit, E has been destroyed.






									Page 1






SSTEDC(3F)							    SSTEDC(3F)



     Z	     (input/output) REAL array,	dimension (LDZ,N)
	     On	entry, if COMPZ	= 'V', then Z contains the orthogonal matrix
	     used in the reduction to tridiagonal form.	 On exit, if INFO = 0,
	     then if COMPZ = 'V', Z contains the orthonormal eigenvectors of
	     the original symmetric matrix, and	if COMPZ = 'I',	Z contains the
	     orthonormal eigenvectors of the symmetric tridiagonal matrix.  If
	     COMPZ = 'N', then Z is not	referenced.

     LDZ     (input) INTEGER
	     The leading dimension of the array	Z.  LDZ	>= 1.  If eigenvectors
	     are desired, then LDZ >= max(1,N).

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

     LWORK   (input) INTEGER
	     The dimension of the array	WORK.  If COMPZ	= 'N' or N <= 1	then
	     LWORK must	be at least 1.	If COMPZ = 'V' and N > 1 then LWORK
	     must be at	least (	1 + 3*N	+ 2*N*lg N + 3*N**2 ), where lg( N ) =
	     smallest integer k	such that 2**k >= N.  If COMPZ = 'I' and N > 1
	     then LWORK	must be	at least ( 1 + 3*N + 2*N*lg N +	2*N**2 ).

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

     LIWORK  (input) INTEGER
	     The dimension of the array	IWORK.	If COMPZ = 'N' or N <= 1 then
	     LIWORK must be at least 1.	 If COMPZ = 'V'	and N >	1 then LIWORK
	     must be at	least (	6 + 6*N	+ 5*N*lg N ).  If COMPZ	= 'I' and N >
	     1 then LIWORK must	be at least ( 2	+ 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).


									PPPPaaaaggggeeee 2222
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