lasd3 - Man Page

lasd3: D&C step: secular equation

subroutine dlasd3 (nl, nr, sqre, k, d, q, ldq, dsigma, u, ldu, u2, ldu2, vt, ldvt, vt2, ldvt2, idxc, ctot, z, info)
DLASD3 finds all square roots of the roots of the secular equation, as defined by the values in D and Z, and then updates the singular vectors by matrix multiplication. Used by sbdsdc.
subroutine slasd3 (nl, nr, sqre, k, d, q, ldq, dsigma, u, ldu, u2, ldu2, vt, ldvt, vt2, ldvt2, idxc, ctot, z, info)
SLASD3 finds all square roots of the roots of the secular equation, as defined by the values in D and Z, and then updates the singular vectors by matrix multiplication. Used by sbdsdc.

Detailed Description

Function Documentation

subroutine dlasd3 (integer nl, integer nr, integer sqre, integer k, double precision, dimension( * ) d, double precision, dimension( ldq, * ) q, integer ldq, double precision, dimension( * ) dsigma, double precision, dimension( ldu, * ) u, integer ldu, double precision, dimension( ldu2, * ) u2, integer ldu2, double precision, dimension( ldvt, * ) vt, integer ldvt, double precision, dimension( ldvt2, * ) vt2, integer ldvt2, integer, dimension( * ) idxc, integer, dimension( * ) ctot, double precision, dimension( * ) z, integer info)

DLASD3 finds all square roots of the roots of the secular equation, as defined by the values in D and Z, and then updates the singular vectors by matrix multiplication. Used by sbdsdc.

Purpose:

 DLASD3 finds all the square roots of the roots of the secular
 equation, as defined by the values in D and Z.  It makes the
 appropriate calls to DLASD4 and then updates the singular
 vectors by matrix multiplication.

 DLASD3 is called from DLASD1.

Parameters

          NL is INTEGER
         The row dimension of the upper block.  NL >= 1.

          NR is INTEGER
         The row dimension of the lower block.  NR >= 1.

SQRE

          SQRE is INTEGER
         = 0: the lower block is an NR-by-NR square matrix.
         = 1: the lower block is an NR-by-(NR+1) rectangular matrix.

         The bidiagonal matrix has N = NL + NR + 1 rows and
         M = N + SQRE >= N columns.

          K is INTEGER
         The size of the secular equation, 1 =< K = < N.

          D is DOUBLE PRECISION array, dimension(K)
         On exit the square roots of the roots of the secular equation,
         in ascending order.

          Q is DOUBLE PRECISION array, dimension (LDQ,K)

LDQ

          LDQ is INTEGER
         The leading dimension of the array Q.  LDQ >= K.

DSIGMA

          DSIGMA is 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.

          U is DOUBLE PRECISION array, dimension (LDU, N)
         The last N - K columns of this matrix contain the deflated
         left singular vectors.

LDU

          LDU is INTEGER
         The leading dimension of the array U.  LDU >= N.

          U2 is DOUBLE PRECISION array, dimension (LDU2, N)
         The first K columns of this matrix contain the non-deflated
         left singular vectors for the split problem.

LDU2

          LDU2 is INTEGER
         The leading dimension of the array U2.  LDU2 >= N.

          VT is DOUBLE PRECISION array, dimension (LDVT, M)
         The last M - K columns of VT**T contain the deflated
         right singular vectors.

LDVT

          LDVT is INTEGER
         The leading dimension of the array VT.  LDVT >= N.

VT2

          VT2 is DOUBLE PRECISION array, dimension (LDVT2, N)
         The first K columns of VT2**T contain the non-deflated
         right singular vectors for the split problem.

LDVT2

          LDVT2 is INTEGER
         The leading dimension of the array VT2.  LDVT2 >= N.

IDXC

          IDXC is INTEGER array, dimension ( N )
         The permutation used to arrange the columns of U (and rows of
         VT) into three groups:  the first group contains non-zero
         entries only at and above (or before) NL +1; the second
         contains non-zero entries only at and below (or after) NL+2;
         and the third is dense. The first column of U and the row of
         VT are treated separately, however.

         The rows of the singular vectors found by DLASD4
         must be likewise permuted before the matrix multiplies can
         take place.

CTOT

          CTOT is INTEGER array, dimension ( 4 )
         A count of the total number of the various types of columns
         in U (or rows in VT), as described in IDXC. The fourth column
         type is any column which has been deflated.

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

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.

Contributors:

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

Definition at line 214 of file dlasd3.f.

subroutine slasd3 (integer nl, integer nr, integer sqre, integer k, real, dimension( * ) d, real, dimension( ldq, * ) q, integer ldq, real, dimension( * ) dsigma, real, dimension( ldu, * ) u, integer ldu, real, dimension( ldu2, * ) u2, integer ldu2, real, dimension( ldvt, * ) vt, integer ldvt, real, dimension( ldvt2, * ) vt2, integer ldvt2, integer, dimension( * ) idxc, integer, dimension( * ) ctot, real, dimension( * ) z, integer info)

SLASD3 finds all square roots of the roots of the secular equation, as defined by the values in D and Z, and then updates the singular vectors by matrix multiplication. Used by sbdsdc.