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

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