Contents

# p?syr2

Performs a rank-2 update of a distributed symmetric matrix.

## Syntax

Include Files
• mkl_pblas.h
Description
The
p?syr2
routines perform a distributed matrix-vector operation defined as
`sub(A) := alpha*sub(x)*sub(y)'+ alpha*sub(y)*sub(x)' + sub(A),`
where:
alpha
is a scalar,
sub(
A
)
is a
n
-by-
n
distributed symmetric matrix,
sub(
A
)=
A
(
ia
:
ia
+
n
-1,
ja
:
ja
+
n
-1)
,
sub(
x
)
and
sub(
y
)
are distributed vectors.
sub(
x
)
denotes
X
(
ix
,
jx
:
jx
+
n
-1)
if
incx
=
m_x
, and
X
(
ix
:
ix
+
n
-1,
jx
)
if
incx
= 1,
sub(
y
)
denotes
Y
(
iy
,
jy
:
jy
+
n
-1)
if
incy
=
m_y
, and
Y
(
iy
:
iy
+
n
-1,
jy
)
if
incy
= 1
.
Input Parameters
uplo
(global) Specifies whether the upper or lower triangular part of the distributed symmetric matrix
sub(
A
)
is used:
If
uplo
=
'U'
or
'u'
, then the upper triangular part of the
sub(
A
)
is used.
If
uplo
=
'L'
or
'l'
, then the low triangular part of the
sub(
A
)
is used.
n
(global) Specifies the order of the distributed matrix
sub(
A
)
,
n
0.
alpha
(global)
Specifies the scalar
alpha
.
x
(local)
Array, size at least
(
jx
-1)*
m_x
+
ix
+(
n
-1)*abs(
incx
))
.
This array contains the entries of the distributed vector
sub(
x
)
.
ix
,
jx
(global) The row and column indices in the distributed matrix
X
indicating the first row and the first column of the submatrix
sub(
x
)
, respectively.
descx
(global and local) array of dimension 9. The array descriptor of the distributed matrix
X
.
incx
(global) Specifies the increment for the elements of
sub(
x
)
. Only two values are supported, namely 1 and
m_x
.
incx
must not be zero.
y
(local)
Array, size at least
(
jy
-1)*
m_y
+
iy
+(
n
-1)*abs(
incy
))
.
This array contains the entries of the distributed vector
sub(
y
)
.
iy
,
jy
(global) The row and column indices in the distributed matrix
Y
indicating the first row and the first column of the submatrix
sub(
y
)
, respectively.
descy
(global and local) array of dimension 9. The array descriptor of the distributed matrix
Y
.
incy
(global) Specifies the increment for the elements of
sub(
y
)
. Only two values are supported, namely 1 and
m_y
.
incy
must not be zero.
a
(local)
Array, size
(
lld_a
, LOCq(
ja
+
n
-1))
. This array contains the local pieces of the distributed matrix
sub(
A
)
.
Before entry with
uplo
=
'U'
or
'u'
, the
n
-by-
n
upper triangular part of the distributed matrix
sub(
A
)
must contain the upper triangular part of the distributed symmetric matrix and the strictly lower triangular part of
sub(
A
)
is not referenced, and with
uplo
=
'L'
or
'l'
, the
n
-by-
n
lower triangular part of the distributed matrix
sub(
A
)
must contain the lower triangular part of the distributed symmetric matrix and the strictly upper triangular part of
sub(
A
)
is not referenced.
ia
,
ja
(global) The row and column indices in the distributed matrix
A
indicating the first row and the first column of the submatrix
sub(
A
)
, respectively.
desca
(global and local) array of dimension 9. The array descriptor of the distributed matrix
A
.
Output Parameters
a
With
uplo
=
'U'
or
'u'
, the upper triangular part of the array
a
is overwritten by the upper triangular part of the updated distributed matrix
sub(
A
)
.
With
uplo
=
'L'
or
'l'
, the lower triangular part of the array
a
is overwritten by the lower triangular part of the updated distributed matrix
sub(
A
)
.

#### 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