Developer Reference

  • 0.9
  • 09/09/2020
  • Public Content
Contents

p?larfg

Generates an elementary reflector (Householder matrix).

Syntax

void
pslarfg
(
MKL_INT
*n
,
float
*alpha
,
MKL_INT
*iax
,
MKL_INT
*jax
,
float
*x
,
MKL_INT
*ix
,
MKL_INT
*jx
,
MKL_INT
*descx
,
MKL_INT
*incx
,
float
*tau
);
void
pdlarfg
(
MKL_INT
*n
,
double
*alpha
,
MKL_INT
*iax
,
MKL_INT
*jax
,
double
*x
,
MKL_INT
*ix
,
MKL_INT
*jx
,
MKL_INT
*descx
,
MKL_INT
*incx
,
double
*tau
);
void
pclarfg
(
MKL_INT
*n
,
MKL_Complex8
*alpha
,
MKL_INT
*iax
,
MKL_INT
*jax
,
MKL_Complex8
*x
,
MKL_INT
*ix
,
MKL_INT
*jx
,
MKL_INT
*descx
,
MKL_INT
*incx
,
MKL_Complex8
*tau
);
void
pzlarfg
(
MKL_INT
*n
,
MKL_Complex16
*alpha
,
MKL_INT
*iax
,
MKL_INT
*jax
,
MKL_Complex16
*x
,
MKL_INT
*ix
,
MKL_INT
*jx
,
MKL_INT
*descx
,
MKL_INT
*incx
,
MKL_Complex16
*tau
);
Include Files
  • mkl_scalapack.h
Description
The
p?larfg
function
generates a real/complex elementary reflector
H
of order
n
, such that
where
alpha
is a scalar (a real scalar - for complex flavors), and sub(
X
) is an (
n
-1)-element real/complex distributed vector
X
(
ix
:
ix
+
n
-2,
jx
)
if
incx
= 1
and
X
(
ix
,
jx
:
jx
+
n
-2)
if
incx
=
m_x
.
H
is represented in the form
where
tau
is a real/complex scalar and
v
is a real/complex (
n
-1)-element vector. Note that
H
is not Hermitian.
If the elements of sub(
X
) are all zero (and
X
(
iax
,
jax
)
is real for complex flavors), then
tau
= 0
and
H
is taken to be the unit matrix.
Otherwise and
abs(
tau
-1) ≤ 1
.
Input Parameters
n
(global)
The global order of the elementary reflector.
n
0
.
iax
,
jax
(global)
The global row and column indices of
X
(
iax
,
jax
)
in the global matrix
X
.
x
(local).
Pointer into the local memory to an array of size
lld_x
*
LOCc
(
n_x
)
. This array contains the local pieces of the distributed vector sub(
X
). Before entry, the incremented array sub(
X
) must contain vector
x
.
ix
,
jx
(global)
The row and column indices in the global matrix
X
indicating the first row and the first column of sub(
X
), respectively.
descx
(global and local)
Array of size
dlen_
. The array descriptor for the distributed matrix
X
.
incx
(global)
The global increment for the elements of
x
. Only two values of
incx
are supported in this version, namely 1 and
m_x
.
incx
must not be zero.
Output Parameters
alpha
(local)
On exit,
alpha
is computed in the process scope having the vector sub(
X
).
x
(local).
On exit, it is overwritten with the vector
v
.
tau
(local).
Array of size
LOCc
(
jx
) if
incx
= 1
, and
LOCr
(
ix
)
otherwise. This array contains the Householder scalars related to the Householder vectors.
tau
is tied to the distributed matrix
X
.

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