Contents

# p?gemv

Computes a distributed matrix-vector product using a general matrix.

## Syntax

Include Files
• mkl_pblas.h
Description
The
p?gemv
routines perform a distributed matrix-vector operation defined as
`sub(y)  := alpha*sub(A)*sub(x) + beta*sub(y),`
or
`sub(y)  := alpha*sub(A)'*sub(x) + beta*sub(y),`
or
`sub(y)  := alpha*conjg(sub(A)')*sub(x) + beta*sub(y),`
where
alpha
and
beta
are scalars,
sub(
A
) is a
m
-by-
n
submatrix,
sub(
A
) =
A
(
ia
:
ia
+
m
-1,
ja
:
ja
+
n
-1)
,
sub(
x
)
and
sub(
y
)
are subvectors.
When
trans
= '
N
'
or
'
n
'
,
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
+
m
-1)
if
incy
=
m_y
, and
Y
(
iy
:
iy
+
m
-1,
jy
)
if
incy
= 1
.
When
trans
= '
T
'
or
'
t
'
, or
'
C
'
, or
'
c
'
,
sub(
x
)
denotes
X
(
ix
,
jx
:
jx
+
m
-1)
if
incx
=
m_x
, and
X
(
ix
:
ix
+
m
-1,
jx
)
if
incx
= 1,
sub(
y
)
denotes
Y
(
iy
,
jy
:
jy
+
n
-1)
if
incy
=
m_y
, and
Y
(
iy
:
iy
+
m
-1,
jy
)
if
incy
= 1
.
Input Parameters
trans
(global) Specifies the operation:
if
trans
= '
N
'
or
'
n
'
, then
sub(
y
) :=
alpha
*sub(
A
)'*sub(
x
) +
beta
*sub(
y
)
;
if
trans
= '
T
'
or
'
t
'
, then
sub(
y
) :=
alpha
*sub(
A
)'*sub(
x
) +
beta
*sub(
y
)
;
if
trans
= '
C
'
or
'
c
'
, then
sub(
y
) :=
alpha
*conjg(sub
A
)')*sub(
x
) +
beta
*sub(
y
)
.
m
(global) Specifies the number of rows of the distributed matrix
sub(
A
)
,
m
0.
n
(global) Specifies the number of columns of the distributed matrix
sub(
A
)
,
n
0.
alpha
(global)
Specifies the scalar
alpha
.
a
(local)
Array, size
(
lld_a
, LOCq(
ja
+
n
-1))
. Before entry this array must contain the local pieces of the distributed matrix
sub(
A
)
.
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
(
jx
-1)*
m_x
+
ix
+(
n
-1)*abs(
incx
))
when
trans
= '
N
'
or
'n'
, and
(
jx
-1)*
m_x
+
ix
+(
m
-1)*abs(
incx
))
otherwise.
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
(
jy
-1)*
m_y
+
iy
+(
m
-1)*abs(
incy
))
when
trans
= '
N
'
or
'n'
, and
(
jy
-1)*
m_y
+
iy
+(
n
-1)*abs(
incy
))
otherwise.
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

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