
dlasd2.f(3) LAPACK dlasd2.f(3)
NAME
dlasd2.f 
SYNOPSIS
Functions/Subroutines
subroutine dlasd2 (NL, NR, SQRE, K, D, Z, ALPHA, BETA, U, LDU, VT, LDVT, DSIGMA, U2, LDU2,
VT2, LDVT2, IDXP, IDX, IDXC, IDXQ, COLTYP, INFO)
DLASD2 merges the two sets of singular values together into a single sorted set. Used
by sbdsdc.
Function/Subroutine Documentation
subroutine dlasd2 (integerNL, integerNR, integerSQRE, integerK, double precision, dimension( *
)D, double precision, dimension( * )Z, double precisionALPHA, double precisionBETA, double
precision, dimension( ldu, * )U, integerLDU, double precision, dimension( ldvt, * )VT,
integerLDVT, double precision, dimension( * )DSIGMA, double precision, dimension( ldu2, *
)U2, integerLDU2, double precision, dimension( ldvt2, * )VT2, integerLDVT2, integer,
dimension( * )IDXP, integer, dimension( * )IDX, integer, dimension( * )IDXC, integer,
dimension( * )IDXQ, integer, dimension( * )COLTYP, integerINFO)
DLASD2 merges the two sets of singular values together into a single sorted set. Used by
sbdsdc.
Purpose:
DLASD2 merges the two sets of singular values 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
singular values are close together or if there is a tiny entry in the
Z vector. For each such occurrence the order of the related secular
equation problem is reduced by one.
DLASD2 is called from DLASD1.
Parameters:
NL
NL is INTEGER
The row dimension of the upper block. NL >= 1.
NR
NR is INTEGER
The row dimension of the lower block. NR >= 1.
SQRE
SQRE is INTEGER
= 0: the lower block is an NRbyNR square matrix.
= 1: the lower block is an NRby(NR+1) rectangular matrix.
The bidiagonal matrix has N = NL + NR + 1 rows and
M = N + SQRE >= N columns.
K
K is INTEGER
Contains the dimension of the nondeflated matrix,
This is the order of the related secular equation. 1 <= K <=N.
D
D is DOUBLE PRECISION array, dimension(N)
On entry D contains the singular values of the two submatrices
to be combined. On exit D contains the trailing (NK) updated
singular values (those which were deflated) sorted into
increasing order.
Z
Z is DOUBLE PRECISION array, dimension(N)
On exit Z contains the updating row vector in the secular
equation.
ALPHA
ALPHA is DOUBLE PRECISION
Contains the diagonal element associated with the added row.
BETA
BETA is DOUBLE PRECISION
Contains the offdiagonal element associated with the added
row.
U
U is DOUBLE PRECISION array, dimension(LDU,N)
On entry U contains the left singular vectors of two
submatrices in the two square blocks with corners at (1,1),
(NL, NL), and (NL+2, NL+2), (N,N).
On exit U contains the trailing (NK) updated left singular
vectors (those which were deflated) in its last NK columns.
LDU
LDU is INTEGER
The leading dimension of the array U. LDU >= N.
VT
VT is DOUBLE PRECISION array, dimension(LDVT,M)
On entry VT**T contains the right singular vectors of two
submatrices in the two square blocks with corners at (1,1),
(NL+1, NL+1), and (NL+2, NL+2), (M,M).
On exit VT**T contains the trailing (NK) updated right singular
vectors (those which were deflated) in its last NK columns.
In case SQRE =1, the last row of VT spans the right null
space.
LDVT
LDVT is INTEGER
The leading dimension of the array VT. LDVT >= M.
DSIGMA
DSIGMA is DOUBLE PRECISION array, dimension (N)
Contains a copy of the diagonal elements (K1 singular values
and one zero) in the secular equation.
U2
U2 is DOUBLE PRECISION array, dimension(LDU2,N)
Contains a copy of the first K1 left singular vectors which
will be used by DLASD3 in a matrix multiply (DGEMM) to solve
for the new left singular vectors. U2 is arranged into four
blocks. The first block contains a column with 1 at NL+1 and
zero everywhere else; the second block contains nonzero
entries only at and above NL; the third contains nonzero
entries only below NL+1; and the fourth is dense.
LDU2
LDU2 is INTEGER
The leading dimension of the array U2. LDU2 >= N.
VT2
VT2 is DOUBLE PRECISION array, dimension(LDVT2,N)
VT2**T contains a copy of the first K right singular vectors
which will be used by DLASD3 in a matrix multiply (DGEMM) to
solve for the new right singular vectors. VT2 is arranged into
three blocks. The first block contains a row that corresponds
to the special 0 diagonal element in SIGMA; the second block
contains nonzeros only at and before NL +1; the third block
contains nonzeros only at and after NL +2.
LDVT2
LDVT2 is INTEGER
The leading dimension of the array VT2. LDVT2 >= M.
IDXP
IDXP is INTEGER array dimension(N)
This will contain the permutation used to place deflated
values of D at the end of the array. On output IDXP(2:K)
points to the nondeflated Dvalues and IDXP(K+1:N)
points to the deflated singular values.
IDX
IDX is INTEGER array dimension(N)
This will contain the permutation used to sort the contents of
D into ascending order.
IDXC
IDXC is INTEGER array dimension(N)
This will contain the permutation used to arrange the columns
of the deflated U matrix into three groups: the first group
contains nonzero entries only at and above NL, the second
contains nonzero entries only below NL+2, and the third is
dense.
IDXQ
IDXQ is INTEGER array dimension(N)
This contains the permutation which separately sorts the two
subproblems in D into ascending order. Note that entries in
the first hlaf of this permutation must first be moved one
position backward; and entries in the second half
must first have NL+1 added to their values.
COLTYP
COLTYP is INTEGER array dimension(N)
As workspace, this will contain a label which will indicate
which of the following types a column in the U2 matrix or a
row in the VT2 matrix is:
1 : nonzero in the upper half only
2 : nonzero in the lower half only
3 : dense
4 : deflated
On exit, it is an array of dimension 4, with COLTYP(I) being
the dimension of the Ith type columns.
INFO
INFO is INTEGER
= 0: successful exit.
< 0: if INFO = i, the ith argument had an illegal value.
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 268 of file dlasd2.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dlasd2.f(3) 
