Contents

# p?getrf

Computes the
LU
factorization of a general m-by-n distributed matrix.

## Syntax

Include Files
• mkl_scalapack.h
Description
The
p?getrf
function
forms the
LU
factorization of a general
m
-by-
n
distributed matrix sub(
A
) =
A
(
ia
:
ia
+
m
-1,
ja
:
ja
+
n
-1) as
A
=
P*L*U
where
P
is a permutation matrix,
L
is lower triangular with unit diagonal elements (lower trapezoidal if
m
>
n
) and
U
is upper triangular (upper trapezoidal if
m
<
n
).
L
and
U
are stored in sub(
A
).
The
function
uses partial pivoting, with row interchanges.
This
function
supports the Progress Routine feature. See
mkl_progress
for details.
Input Parameters
m
(global) The number of rows in the distributed matrix sub(
A
);
m
0
.
n
(global) The number of columns in the distributed matrix sub(
A
);
n
0
.
a
(local)
Pointer into the local memory to an array of local size
lld_a
*
LOCc
(
ja
+
n
-1)
.
Contains the local pieces of the distributed matrix sub(
A
) to be factored.
ia
,
ja
(global) The row and column indices in the global matrix
A
indicating the first row and the first column of the matrix sub(
A
), respectively.
desca
(global and local) array of size
dlen_
. The array descriptor for the distributed matrix
A
.
Output Parameters
a
Overwritten by local pieces of the factors
L
and
U
from the factorization
A
=
P*L*U
. The unit diagonal elements of
L
are not stored.
ipiv
(local) Array of size
LOCr
(
m_a
)+
mb_a
.
Contains the pivoting information: local row
i
was interchanged with global row
ipiv
[
i
-1]
. This array is tied to the distributed matrix
A
.
info
(global)
If
info
=0
, the execution is successful.
info
< 0
: if the
i
-th argument is an array and the
j-
th entry
, indexed
j
- 1,
info
= -(
i
*100+
j
); if the
i-
th argument is a scalar and had an illegal value, then
info
=
-i
.
If
info
=
i
> 0,
u
ia
+
i
,
ja
+
j
-1
is 0. The factorization has been completed, but the factor
U
is exactly singular. Division by zero will occur if you use the factor
U
for solving a system of linear equations.

#### Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804