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dlasd8 examples
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Man Page Details
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NAME
       DLASD8 - the square roots of the roots of the secular equation,

SYNOPSIS
       SUBROUTINE DLASD8( ICOMPQ, K, D, Z, VF, VL, DIFL, DIFR, LDDIFR, DSIGMA,
                          WORK, INFO )

           INTEGER        ICOMPQ, INFO, K, LDDIFR

           DOUBLE         PRECISION D( * ), DIFL( *  ),  DIFR(  LDDIFR,  *  ),
                          DSIGMA( * ), VF( * ), VL( * ), WORK( * ), Z( * )

  Purpose
  =======

  DLASD8 finds the square roots of the roots of the secular equation,
  as defined by the values in DSIGMA and Z. It makes the appropriate
  calls to DLASD4, and stores, for each  element in D, the distance
  to its two nearest poles (elements in DSIGMA). It also updates
  the arrays VF and VL, the first and last components of all the
  right singular vectors of the original bidiagonal matrix.

  DLASD8 is called from DLASD6.

  Arguments
  =========

  ICOMPQ  (input) INTEGER
          Specifies whether singular vectors are to be computed in
          factored form in the calling routine:
          = 0: Compute singular values only.
          = 1: Compute singular vectors in factored form as well.

  K       (input) INTEGER
          The number of terms in the rational function to be solved
          by DLASD4.  K >= 1.

  D       (output) DOUBLE PRECISION array, dimension ( K )
          On output, D contains the updated singular values.

  Z       (input) DOUBLE PRECISION array, dimension ( K )
          The first K elements of this array contain the components
          of the deflation-adjusted updating row vector.

  VF      (input/output) DOUBLE PRECISION array, dimension ( K )
          On entry, VF contains  information passed through DBEDE8.
          On exit, VF contains the first K components of the first
          components of all right singular vectors of the bidiagonal
          matrix.

  VL      (input/output) DOUBLE PRECISION array, dimension ( K )
          On entry, VL contains  information passed through DBEDE8.
          On exit, VL contains the first K components of the last
          components of all right singular vectors of the bidiagonal
          matrix.

  DIFL    (output) DOUBLE PRECISION array, dimension ( K )
          On exit, DIFL(I) = D(I) - DSIGMA(I).

  DIFR    (output) DOUBLE PRECISION array,
                   dimension ( LDDIFR, 2 ) if ICOMPQ = 1 and
                   dimension ( K ) if ICOMPQ = 0.
          On exit, DIFR(I,1) = D(I) - DSIGMA(I+1), DIFR(K,1) is not
          defined and will not be referenced.

          If ICOMPQ = 1, DIFR(1:K,2) is an array containing the
          normalizing factors for the right singular vector matrix.

  LDDIFR  (input) INTEGER
          The leading dimension of DIFR, must be at least K.

  DSIGMA  (input) DOUBLE PRECISION array, dimension ( K )
          The first K elements of this array contain the old roots
          of the deflated updating problem.  These are the poles
          of the secular equation.

  WORK    (workspace) DOUBLE PRECISION array, dimension at least 3 * K

  INFO    (output) INTEGER
          = 0:  successful exit.
          < 0:  if INFO = -i, the i-th argument had an illegal value.
          > 0:  if INFO = 1, an singular value did not converge

  Further Details
  ===============

  Based on contributions by
     Ming Gu and Huan Ren, Computer Science Division, University of
     California at Berkeley, USA

