## Developer Reference

• 2020.2
• 07/15/2020
• Public Content
Contents

# ?lasd8

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
?bdsdc
.

## Syntax

Include Files
• mkl.fi
Description
The routine
?lasd8
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
?lasd4
, 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.
?lasd8
is called from
?lasd6
.
Input Parameters
icompq
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
INTEGER
.
The number of terms in the rational function to be solved by
?lasd4
.
k
1
.
z
REAL
for
slasd8
DOUBLE PRECISION
for
dlasd8
.
Array,
DIMENSION
(
k
).
The first
k
elements of this array contain the components of the deflation-adjusted updating row vector.
vf
REAL
for
slasd8
DOUBLE PRECISION
for
dlasd8
.
Array,
DIMENSION
(
k
).
On entry,
vf
contains information passed through
dbede8
.
vl
REAL
for
slasd8
DOUBLE PRECISION
for
dlasd8
.
Array,
DIMENSION
(
k
). On entry,
vl
contains information passed through
dbede8
.
lddifr
INTEGER
.
The leading dimension of the output array
difr
, must be at least
k
.
dsigma
REAL
for
slasd8
DOUBLE PRECISION
for
dlasd8
.
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.
work
REAL
for
slasd8
DOUBLE PRECISION
for
dlasd8
.
Workspace array,
DIMENSION
at least (3
k
).
Output Parameters
d
REAL
for
slasd8
DOUBLE PRECISION
for
dlasd8