sstein.f(3)							      LAPACK							       sstein.f(3)

NAME

       sstein.f -

SYNOPSIS

   Functions/Subroutines
       subroutine sstein (N, D, E, M, W, IBLOCK, ISPLIT, Z, LDZ, WORK, IWORK, IFAIL, INFO)
	   SSTEIN

Function/Subroutine Documentation
   subroutine sstein (integerN, real, dimension( * )D, real, dimension( * )E, integerM, real, dimension( * )W, integer, dimension( * )IBLOCK,
       integer, dimension( * )ISPLIT, real, dimension( ldz, * )Z, integerLDZ, real, dimension( * )WORK, integer, dimension( * )IWORK, integer,
       dimension( * )IFAIL, integerINFO)
       SSTEIN

       Purpose:

	    SSTEIN computes the eigenvectors of a real symmetric tridiagonal
	    matrix T corresponding to specified eigenvalues, using inverse
	    iteration.

	    The maximum number of iterations allowed for each eigenvector is
	    specified by an internal parameter MAXITS (currently set to 5).

       Parameters:
	   N

		     N is INTEGER
		     The order of the matrix.  N >= 0.

	   D

		     D is REAL array, dimension (N)
		     The n diagonal elements of the tridiagonal matrix T.

	   E

		     E is REAL array, dimension (N-1)
		     The (n-1) subdiagonal elements of the tridiagonal matrix
		     T, in elements 1 to N-1.

	   M

		     M is INTEGER
		     The number of eigenvectors to be found.  0 <= M <= N.

	   W

		     W is REAL array, dimension (N)
		     The first M elements of W contain the eigenvalues for
		     which eigenvectors are to be computed.  The eigenvalues
		     should be grouped by split-off block and ordered from
		     smallest to largest within the block.  ( The output array
		     W from SSTEBZ with ORDER = 'B' is expected here. )

	   IBLOCK

		     IBLOCK is INTEGER array, dimension (N)
		     The submatrix indices associated with the corresponding
		     eigenvalues in W; IBLOCK(i)=1 if eigenvalue W(i) belongs to
		     the first submatrix from the top, =2 if W(i) belongs to
		     the second submatrix, etc.  ( The output array IBLOCK
		     from SSTEBZ is expected here. )

	   ISPLIT

		     ISPLIT is INTEGER array, dimension (N)
		     The splitting points, at which T breaks up into submatrices.
		     The first submatrix consists of rows/columns 1 to
		     ISPLIT( 1 ), the second of rows/columns ISPLIT( 1 )+1
		     through ISPLIT( 2 ), etc.
		     ( The output array ISPLIT from SSTEBZ is expected here. )

	   Z

		     Z is REAL array, dimension (LDZ, M)
		     The computed eigenvectors.  The eigenvector associated
		     with the eigenvalue W(i) is stored in the i-th column of
		     Z.  Any vector which fails to converge is set to its current
		     iterate after MAXITS iterations.

	   LDZ

		     LDZ is INTEGER
		     The leading dimension of the array Z.  LDZ >= max(1,N).

	   WORK

		     WORK is REAL array, dimension (5*N)

	   IWORK

		     IWORK is INTEGER array, dimension (N)

	   IFAIL

		     IFAIL is INTEGER array, dimension (M)
		     On normal exit, all elements of IFAIL are zero.
		     If one or more eigenvectors fail to converge after
		     MAXITS iterations, then their indices are stored in
		     array IFAIL.

	   INFO

		     INFO is INTEGER
		     = 0: successful exit.
		     < 0: if INFO = -i, the i-th argument had an illegal value
		     > 0: if INFO = i, then i eigenvectors failed to converge
			  in MAXITS iterations.  Their indices are stored in
			  array IFAIL.

       Internal Parameters:

	     MAXITS  INTEGER, default = 5
		     The maximum number of iterations performed.

	     EXTRA   INTEGER, default = 2
		     The number of iterations performed after norm growth
		     criterion is satisfied, should be at least 1.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Definition at line 174 of file sstein.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       sstein.f(3)