slasd8.f man page

subroutine slasd8 (ICOMPQ, K, D, Z, VF, VL, DIFL, DIFR, LDDIFR, DSIGMA, WORK, INFO)
SLASD8 finds the square roots of the roots of the secular equation, and stores, for each element in D, the distance to its two nearest poles. Used by sbdsdc.

SLASD8 finds the square roots of the roots of the secular equation, and stores, for each element in D, the distance to its two nearest poles. Used by sbdsdc.  

Purpose:

 SLASD8 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 SLASD4, 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.

 SLASD8 is called from SLASD6.

Parameters:

ICOMPQ

          ICOMPQ is 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

          K is INTEGER
          The number of terms in the rational function to be solved
          by SLASD4.  K >= 1.

D

          D is REAL array, dimension ( K )
          On output, D contains the updated singular values.

Z

          Z is REAL array, dimension ( K )
          On entry, the first K elements of this array contain the
          components of the deflation-adjusted updating row vector.
          On exit, Z is updated.

VF

          VF is REAL 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

          VL is REAL 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

          DIFL is REAL array, dimension ( K )
          On exit, DIFL(I) = D(I) - DSIGMA(I).

DIFR

          DIFR is REAL 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

          LDDIFR is INTEGER
          The leading dimension of DIFR, must be at least K.

DSIGMA

          DSIGMA is REAL array, dimension ( K )
          On entry, the first K elements of this array contain the old
          roots of the deflated updating problem.  These are the poles
          of the secular equation.
          On exit, the elements of DSIGMA may be very slightly altered
          in value.

WORK

          WORK is REAL array, dimension at least 3 * K

INFO

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

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Contributors:

Ming Gu and Huan Ren, Computer Science Division, University of California at Berkeley, USA

Definition at line 166 of file slasd8.f.