Contents

# p?syr

Performs a rank-1 update of a distributed symmetric matrix.

## Syntax

Include Files
• mkl_pblas.h
Description
The
p?syr
routines perform a distributed matrix-vector operation defined as
`sub(A) := alpha*sub(x)*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
)
is distributed vector.
sub(
x
)
denotes
X
(
ix
,
jx
:
jx
+
n
-1)
if
incx
=
m_x
, and
X
(
ix
:
ix
+
n
-1,
jx
)
if
incx
= 1,
Input Parameters
uplo
(global) Specifies whether the upper or lower triangular part of the symmetric distributed 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.
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 symmetric distributed 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 symmetric distributed 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

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.