## Developer Reference

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

# ?latdf

Uses the LU factorization of the
n
-by-
n
matrix computed by
?getc2
and computes a contribution to the reciprocal Dif-estimate.

## Syntax

Include Files
• mkl.fi
Description
The routine
?latdf
uses the
LU
factorization of the
n
-by-
n
matrix
Z
computed by
?getc2
and computes a contribution to the reciprocal Dif-estimate by solving
Z*
x
=
b
for
x
, and choosing the right-hand side
b
such that the norm of
x
is as large as possible. On entry
rhs
=
b
holds the contribution from earlier solved sub-systems, and on return
rhs
=
x
.
The factorization of
Z
returned by
?getc2
has the form
Z
=
P
*
L
*
U
*
Q
, where
P
and
Q
are permutation matrices.
L
is lower triangular with unit diagonal elements and
U
is upper triangular.
Input Parameters
ijob
INTEGER
.
ijob
= 2
: First compute an approximative null-vector
e
of
Z
using
?gecon
,
e
is normalized, and solve for
Z
*
x
=
±
e
-
f
with the sign giving the greater value of 2-norm(
x
). This option is about 5 times as expensive as default.
ijob
2
(default): Local look ahead strategy where all entries of the right-hand side
b
is chosen as either +1 or -1 .
n
INTEGER
. The number of columns of the matrix
Z
.
z
REAL
for
slatdf
/
clatdf
DOUBLE PRECISION
for
dlatdf
/
zlatdf
.
Array,
DIMENSION
(
ldz
,
n
)
On entry, the
LU
part of the factorization of the
n
-by-
n
matrix
Z
computed by
?getc2
:
Z
=
P
*
L
*
U
*
Q
.
ldz
INTEGER
. The leading dimension of the array
Z
.
lda
max(1,
n
)
.
rhs
REAL
for
slatdf
/
clatdf
DOUBLE PRECISION
for
dlatdf
/
zlatdf
.
Array,
DIMENSION
(
n
).
On entry,
rhs
contains contributions from other subsystems.
rdsum
REAL
for
slatdf
/
clatdf
DOUBLE PRECISION
for
dlatdf
/
zlatdf
.
On entry, the sum of squares of computed contributions to the
D
if-estimate under computation by
?tgsyL
, where the scaling factor
rdscal
has been factored out. If
trans
=
'T'
,
rdsum
is not touched.
Note that
rdsum
only makes sense when
?tgsy2
is called by
?tgsyL
.
rdscal
REAL
for
sl