Contents

# p?potrs

Solves a system of linear equations with a Cholesky-factored symmetric/Hermitian distributed positive-definite matrix.

## Syntax

Include Files
• mkl_scalapack.h
Description
The
p?potrs
function
solves for
X
a system of distributed linear equations in the form:
sub(
A
)*
X
= sub(
B
) ,
where sub(
A
) =
A
(
ia
:
ia
+
n
-1,
ja
:
ja
+
n
-1) is an
n
-by-
n
real symmetric or complex Hermitian positive definite distributed matrix, and sub(
B
) denotes the distributed matrix
B
(
ib
:
ib
+
n
-1,
jb
:
jb
+
nrhs
-1).
This
function
uses Cholesky factorization
sub(
A
) =
U
H
*U
, or sub(
A
) =
L*L
H
computed by
p?potrf
.
Input Parameters
uplo
(global) Must be
'U'
or
'L'
.
If
uplo
=
'U'
, upper triangle of sub(
A
) is stored;
If
uplo
=
'L'
, lower triangle of sub(
A
) is stored.
n
(global) The order of the distributed matrix sub(
A
)
(
n
0)
.
nrhs
(global) The number of right hand sides; the number of columns of the distributed matrix sub(
B
)
(
nrhs
0)
.
a
,
b
(local)
Pointers into the local memory to arrays of local sizes
lld_a
*
LOCc
(
ja
+
n
-1)
and
lld_b
*
LOCc
(
jb
+
nrhs
-1
)
, respectively.
The array
a
contains the factors
L
or
U
from the Cholesky factorization sub(
A
) =
L
*
L
H
or sub(
A
) =
U
H
*U
, as computed by
p?potrf
.
On entry, the array
b
contains the local pieces of the right hand sides sub(
B
).
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
.
ib
,
jb
(global) The row and column indices in the global matrix
B
indicating the first row and the first column of the matrix sub(
B
), respectively.
descb
(local) array of size
dlen_
. The array descriptor for the distributed matrix
B
.
Output Parameters
b
Overwritten by the local pieces of the solution matrix
X
.
info
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
.

#### 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