dsteqr(3) [debian man page]

dsteqr.f(3)							      LAPACK							       dsteqr.f(3)

NAME

       dsteqr.f -

SYNOPSIS

   Functions/Subroutines
       subroutine dsteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO)
	   DSTEQR

Function/Subroutine Documentation
   subroutine dsteqr (characterCOMPZ, integerN, double precision, dimension( * )D, double precision, dimension( * )E, double precision, dimension(
       ldz, * )Z, integerLDZ, double precision, dimension( * )WORK, integerINFO)
       DSTEQR

       Purpose:

	    DSTEQR computes all eigenvalues and, optionally, eigenvectors of a
	    symmetric tridiagonal matrix using the implicit QL or QR method.
	    The eigenvectors of a full or band symmetric matrix can also be found
	    if DSYTRD or DSPTRD or DSBTRD has been used to reduce this matrix to
	    tridiagonal form.

       Parameters:
	   COMPZ

		     COMPZ is CHARACTER*1
		     = 'N':  Compute eigenvalues only.
		     = 'V':  Compute eigenvalues and eigenvectors of the original
			     symmetric matrix.	On entry, Z must contain the
			     orthogonal matrix used to reduce the original matrix
			     to tridiagonal form.
		     = 'I':  Compute eigenvalues and eigenvectors of the
			     tridiagonal matrix.  Z is initialized to the identity
			     matrix.

	   N

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

	   D

		     D is DOUBLE PRECISION array, dimension (N)
		     On entry, the diagonal elements of the tridiagonal matrix.
		     On exit, if INFO = 0, the eigenvalues in ascending order.

	   E

		     E is DOUBLE PRECISION array, dimension (N-1)
		     On entry, the (n-1) subdiagonal elements of the tridiagonal
		     matrix.
		     On exit, E has been destroyed.

	   Z

		     Z is DOUBLE PRECISION 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

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

	   WORK

		     WORK is DOUBLE PRECISION array, dimension (max(1,2*N-2))
		     If COMPZ = 'N', then WORK is not referenced.

	   INFO

		     INFO is INTEGER
		     = 0:  successful exit
		     < 0:  if INFO = -i, the i-th argument had an illegal value
		     > 0:  the algorithm has failed to find all the eigenvalues in
			   a total of 30*N iterations; if INFO = i, then i
			   elements of E have not converged to zero; on exit, D
			   and E contain the elements of a symmetric tridiagonal
			   matrix which is orthogonally similar to the original
			   matrix.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Definition at line 132 of file dsteqr.f.

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

Version 3.4.1							  Sun May 26 2013						       dsteqr.f(3)