SRC/slaed8.f(3)

NAME
SRC/slaed8.f

SYNOPSIS

  Functions/Subroutines
subroutine slaed8 (icompq, k, n, qsiz, d, q, ldq, indxq, rho, cutpnt, z, dlambda, q2, ldq2, w, perm, givptr, givcol, givnum, indxp, indx, info)
SLAED8 used by SSTEDC. Merges eigenvalues and deflates secular equation. Used when the original matrix is dense.

Function/Subroutine Documentation

  subroutine slaed8 (integer icompq, integer k, integer n, integer qsiz, real, dimension( * ) d, real, dimension( ldq, * ) q, integer ldq, integer, dimension( * ) indxq, real rho, integer cutpnt, real, dimension( * ) z, real, dimension( * ) dlambda, real, dimension( ldq2, * ) q2, integer ldq2, real, dimension( * ) w, integer, dimension( * ) perm, integer givptr, integer, dimension( 2, * ) givcol, real, dimension( 2, * ) givnum, integer, dimension( * ) indxp, integer, dimension( * ) indx, integer info)

SLAED8 used by SSTEDC. Merges eigenvalues and deflates secular equation. Used when the original matrix is dense.

Purpose:

    !>
    !> SLAED8 merges the two sets of eigenvalues together into a single
    !> sorted set.  Then it tries to deflate the size of the problem.
    !> There are two ways in which deflation can occur:  when two or more
    !> eigenvalues are close together or if there is a tiny element in the
    !> Z vector.  For each such occurrence the order of the related secular
    !> equation problem is reduced by one.
    !>

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.
    !>

    K

    !>          K is INTEGER
    !>         The number of non-deflated eigenvalues, and the order of the
    !>         related secular equation.
    !>

    N

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

    QSIZ

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

    D

    !>          D is REAL array, dimension (N)
    !>         On entry, the eigenvalues of the two submatrices to be
    !>         combined.  On exit, the trailing (N-K) updated eigenvalues
    !>         (those which were deflated) sorted into increasing order.
    !>

    Q

    !>          Q is REAL array, dimension (LDQ,N)
    !>         If ICOMPQ = 0, Q is not referenced.  Otherwise,
    !>         on entry, Q contains the eigenvectors of the partially solved
    !>         system which has been previously updated in matrix
    !>         multiplies with other partially solved eigensystems.
    !>         On exit, Q contains the trailing (N-K) updated eigenvectors
    !>         (those which were deflated) in its last N-K columns.
    !>

    LDQ

    !>          LDQ is INTEGER
    !>         The leading dimension of the array Q.  LDQ >= max(1,N).
    !>

    INDXQ

    !>          INDXQ is INTEGER array, dimension (N)
    !>         The permutation which separately sorts the two sub-problems
    !>         in D into ascending order.  Note that elements in the second
    !>         half of this permutation must first have CUTPNT added to
    !>         their values in order to be accurate.
    !>

    RHO

    !>          RHO is REAL
    !>         On entry, the off-diagonal element associated with the rank-1
    !>         cut which originally split the two submatrices which are now
    !>         being recombined.
    !>         On exit, RHO has been modified to the value required by
    !>         SLAED3.
    !>

    CUTPNT

    !>          CUTPNT is INTEGER
    !>         The location of the last eigenvalue in the leading
    !>         sub-matrix.  min(1,N) <= CUTPNT <= N.
    !>

    Z

    !>          Z is REAL array, dimension (N)
    !>         On entry, Z contains the updating vector (the last row of
    !>         the first sub-eigenvector matrix and the first row of the
    !>         second sub-eigenvector matrix).
    !>         On exit, the contents of Z are destroyed by the updating
    !>         process.
    !>

    DLAMBDA

    !>          DLAMBDA is REAL array, dimension (N)
    !>         A copy of the first K eigenvalues which will be used by
    !>         SLAED3 to form the secular equation.
    !>

    Q2

    !>          Q2 is REAL array, dimension (LDQ2,N)
    !>         If ICOMPQ = 0, Q2 is not referenced.  Otherwise,
    !>         a copy of the first K eigenvectors which will be used by
    !>         SLAED7 in a matrix multiply (SGEMM) to update the new
    !>         eigenvectors.
    !>

    LDQ2

    !>          LDQ2 is INTEGER
    !>         The leading dimension of the array Q2.  LDQ2 >= max(1,N).
    !>

    W

    !>          W is REAL array, dimension (N)
    !>         The first k values of the final deflation-altered z-vector and
    !>         will be passed to SLAED3.
    !>

    PERM

    !>          PERM is INTEGER array, dimension (N)
    !>         The permutations (from deflation and sorting) to be applied
    !>         to each eigenblock.
    !>

    GIVPTR

    !>          GIVPTR is INTEGER
    !>         The number of Givens rotations which took place in this
    !>         subproblem.
    !>

    GIVCOL

    !>          GIVCOL is INTEGER array, dimension (2, N)
    !>         Each pair of numbers indicates a pair of columns to take place
    !>         in a Givens rotation.
    !>

    GIVNUM

    !>          GIVNUM is REAL array, dimension (2, N)
    !>         Each number indicates the S value to be used in the
    !>         corresponding Givens rotation.
    !>

    INDXP

    !>          INDXP is INTEGER array, dimension (N)
    !>         The permutation used to place deflated values of D at the end
    !>         of the array.  INDXP(1:K) points to the nondeflated D-values
    !>         and INDXP(K+1:N) points to the deflated eigenvalues.
    !>

    INDX

    !>          INDX is INTEGER array, dimension (N)
    !>         The permutation used to sort the contents of D into ascending
    !>         order.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit.
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

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

Definition at line 240 of file slaed8.f.

Author

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