Contents

# p?ahemv

Computes a distributed matrix-vector product using absolute values for a Hermitian matrix.

## Syntax

Include Files
• mkl_pblas.h
Description
The
p?ahemv
routines perform a distributed matrix-vector operation defined as
sub(y) := abs(alpha)*abs(sub(A))*abs(sub(x)) + abs(beta*sub(y)),
where:
alpha
and
beta
are scalars,
sub(
A
)
is a
n
-by-
n
Hermitian distributed 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 Hermitian 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
.
a
(local)
Array, size
(
lld_a
, LOCq(
ja
+
n
-1))
. This array contains the local pieces of the distributed matrix
sub(
A
)
.
Before entry when
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 Hermitian distributed matrix and the strictly lower triangular part of
sub(
A
)
is not referenced, and when
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 Hermitian 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
.
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.
beta
(global)
Specifies the scalar
beta
. When
beta
is set to zero, then
sub(
y
)
need not be set on input.
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.
Output Parameters
y
Overwritten by the updated distributed vector
sub(
y
)
.

#### Product and Performance Information

1

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