SRC/dsteqr.f(3)            Library Functions Manual            SRC/dsteqr.f(3)

NAME
       SRC/dsteqr.f

SYNOPSIS
   Functions/Subroutines
       subroutine dsteqr (compz, n, d, e, z, ldz, work, info)
           DSTEQR

Function/Subroutine Documentation
   subroutine dsteqr (character compz, integer n, double precision, dimension(
       * ) d, double precision, dimension( * ) e, double precision, dimension(
       ldz, * ) z, integer ldz, double precision, dimension( * ) work, integer
       info)
       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.

       Definition at line 130 of file dsteqr.f.

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

LAPACK                          Version 3.12.0                 SRC/dsteqr.f(3)