dlasd8.f (3) Linux Manual Page

dlasd8.f –

Synopsis

Functions/Subroutines

subroutine dlasd8 (ICOMPQ, K, D, Z, VF, VL, DIFL, DIFR, LDDIFR, DSIGMA, WORK, INFO)
DLASD8 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.

Function/Subroutine Documentation

subroutine dlasd8 (integerICOMPQ, integerK, double precision, dimension( * )D, double precision, dimension( * )Z, double precision, dimension( * )VF, double precision, dimension( * )VL, double precision, dimension( * )DIFL, double precision, dimension( lddifr, * )DIFR, integerLDDIFR, double precision, dimension( * )DSIGMA, double precision, dimension( * )WORK, integerINFO)

DLASD8 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:

 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.

 

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 DLASD4. K >= 1.

D

 D is DOUBLE PRECISION array, dimension ( K )

 On output, D contains the updated singular values.

Z

 Z is DOUBLE PRECISION 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 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

 VL is 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

 DIFL is DOUBLE PRECISION array, dimension ( K )

 On exit, DIFL(I) = D(I) – DSIGMA(I).

DIFR

 DIFR is 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

 LDDIFR is INTEGER

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

DSIGMA

 DSIGMA is DOUBLE PRECISION 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 DOUBLE PRECISION 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 dlasd8.f.

Author

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