Contents

# ?lasd2

Merges the two sets of singular values together into a single sorted set. Used by
?bdsdc
.

## Syntax

Include Files
• mkl.h
Description
The routine
?lasd2
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.
The routine
?lasd2
is called from
?lasd1
.
Input Parameters
nl
The row dimension of the upper block.
nl
1
.
nr
The row dimension of the lower block.
nr
1
.
sqre
If
sqre
= 0
): the lower block is an
nr
-by-
nr
square matrix
If
sqre
= 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.
d
Array,
DIMENSION
(
n
). On entry
d
contains the singular values of the two submatrices to be combined.
alpha
Contains the diagonal element associated with the added row.
beta
Contains the off-diagonal element associated with the added row.
u
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
).
ldu
The leading dimension of the array
u
.
ldu
n
.
ldu2
The leading dimension of the output array
u2
.
ldu2
n
.
vt
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
).
ldvt
The leading dimension of the array
vt
.
ldvt
m
.
ldvt2
The leading dimension of the output array
vt2
.
ldvt2
m
.
idxp
Workspace 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
d
-values and
idxp
(
k
+1:
n
) points to the deflated singular values.
idx
Workspace array,
DIMENSION
(
n
). This will contain the permutation used to sort the contents of
d
into ascending order.
coltyp
Workspace array,
DIMENSION
(
n
). As workspace, this array contains a label that indicates which of the following types a column in the
u2
matrix or a row in the
vt2
matrix is:
1 : non-zero in the upper half only
2 : non-zero in the lower half only
3 : dense
4 : deflated.
idxq
Array,
DIMENSION
(
n
). This parameter contains the permutation that separately sorts the two sub-problems in
D
in the ascending order. Note that entries in the first half of this permutation must first be moved one position backwards and entries in the second half must have
nl
+1
Output Parameters
k
Contains the dimension of the non-deflated matrix, This is the order of the related secular equation.
1 ≤
k
n
.
d
On exit
D
contains the trailing (
n
-
k
) updated singular values (those which were deflated) sorted into increasing order.
u
On exit
u
contains the trailing (
n
-
k
) updated left singular vectors (those which were deflated) in its last
n
-
k
columns.
z
Array,
DIMENSION
(
n
). On exit,
z
contains the updating row vector in the secular equation.
dsigma
Array,
DIMENSION
(
n
). Contains a copy of the diagonal elements (
k
-1
singular values and one zero) in the secular equation.
u2
Array,
DIMENSION
(
ldu2
,
n
). Contains a copy of the first
k
-1
left singular vectors which will be used by
?lasd3
in a matrix multiply (
?gemm
) 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 non-zero entries only at and above
nl
; the third contains non-zero entries only below
nl
+1
; and the fourth is dense.
vt
On exit,
vt
T
contains the trailing (
n
-
k
) updated right singular vectors (those which were deflated) in its last
n
-
k
columns. In case
sqre
=1
, the last row of
vt
spans the right null space.
vt2
Array,
DIMENSION
(
ldvt2
,
n
).
vt2
T
contains a copy of the first
k
right singular vectors which will be used by
?lasd3
in a matrix multiply (
?gemm
) 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 non-zeros only at and before
nl
+1
; the third block contains non-zeros only at and after
nl
+2
.
idxc
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 non-zero entries only at and above
nl
, the second contains non-zero entries only below
nl
+2
, and the third is dense.
coltyp
On exit, it is an array of dimension 4, with
coltyp
(
i
) being the dimension of the
i
-th type columns.
info
If
info
= 0
): successful exit
If
info
= -
i
< 0
, the
i
-th argument had an illegal value.

#### Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.