slaed0.f(3)

NAME
slaed0.f -

SYNOPSIS

  Functions/Subroutines

subroutine slaed0 (ICOMPQ, QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, WORK, IWORK, INFO)
SLAED0 used by sstedc. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Function/Subroutine Documentation

  subroutine slaed0 (integerICOMPQ, integerQSIZ, integerN, real, dimension( * )D, real, dimension( * )E, real, dimension( ldq, * )Q, integerLDQ, real, dimension( ldqs, * )QSTORE, integerLDQS, real, dimension( * )WORK, integer, dimension( * )IWORK, integerINFO)

SLAED0 used by sstedc. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Purpose:

     SLAED0 computes all eigenvalues and corresponding eigenvectors of a
     symmetric tridiagonal matrix using the divide and conquer method.

Parameters:
    ICOMPQ

              ICOMPQ is INTEGER
              = 0:  Compute eigenvalues only.
              = 1:  Compute eigenvectors of original dense symmetric matrix
                    also.  On entry, Q contains the orthogonal matrix used
                    to reduce the original matrix to tridiagonal form.
              = 2:  Compute eigenvalues and eigenvectors of tridiagonal
                    matrix.

    QSIZ

              QSIZ is INTEGER
             The dimension of the orthogonal matrix used to reduce
             the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1.

    N

              N is INTEGER
             The dimension of the symmetric tridiagonal matrix.  N >= 0.

    D

              D is REAL array, dimension (N)
             On entry, the main diagonal of the tridiagonal matrix.
             On exit, its eigenvalues.

    E

              E is REAL array, dimension (N-1)
             The off-diagonal elements of the tridiagonal matrix.
             On exit, E has been destroyed.

    Q

              Q is REAL array, dimension (LDQ, N)
             On entry, Q must contain an N-by-N orthogonal matrix.
             If ICOMPQ = 0    Q is not referenced.
             If ICOMPQ = 1    On entry, Q is a subset of the columns of the
                              orthogonal matrix used to reduce the full
                              matrix to tridiagonal form corresponding to
                              the subset of the full matrix which is being
                              decomposed at this time.
             If ICOMPQ = 2    On entry, Q will be the identity matrix.
                              On exit, Q contains the eigenvectors of the
                              tridiagonal matrix.

    LDQ

              LDQ is INTEGER
             The leading dimension of the array Q.  If eigenvectors are
             desired, then  LDQ >= max(1,N).  In any case,  LDQ >= 1.

    QSTORE

              QSTORE is REAL array, dimension (LDQS, N)
             Referenced only when ICOMPQ = 1.  Used to store parts of
             the eigenvector matrix when the updating matrix multiplies
             take place.

    LDQS

              LDQS is INTEGER
             The leading dimension of the array QSTORE.  If ICOMPQ = 1,
             then  LDQS >= max(1,N).  In any case,  LDQS >= 1.

    WORK

              WORK is REAL array,
             If ICOMPQ = 0 or 1, the dimension of WORK must be at least
                         1 + 3*N + 2*N*lg N + 3*N**2
                         ( lg( N ) = smallest integer k
                                     such that 2^k >= N )
             If ICOMPQ = 2, the dimension of WORK must be at least
                         4*N + N**2.

    IWORK

              IWORK is INTEGER array,
             If ICOMPQ = 0 or 1, the dimension of IWORK must be at least
                            6 + 6*N + 5*N*lg N.
                            ( lg( N ) = smallest integer k
                                        such that 2^k >= N )
             If ICOMPQ = 2, the dimension of IWORK must be at least
                            3 + 5*N.

    INFO

              INFO is 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).

Author:
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Date:
    September 2012

Contributors:
    Jeff Rutter, Computer Science Division, University of California at Berkeley, USA

Definition at line 172 of file slaed0.f.

Author

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