Developer Reference for Intel® oneAPI Math Kernel Library - C

Developer Reference

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

?larfb

Applies a block reflector or its transpose/conjugate-transpose to a general rectangular matrix.

Syntax

lapack_int
LAPACKE_slarfb
(
int
matrix_layout
,
char
side
,
char
trans
,
char
direct
,
char
storev
,
lapack_int
m
,
lapack_int
n
,
lapack_int
k
,
const
float
*
v
,
lapack_int
ldv
,
const
float
*
t
,
lapack_int
ldt
,
float
*
c
,
lapack_int
ldc
);
lapack_int
LAPACKE_dlarfb
(
int
matrix_layout
,
char
side
,
char
trans
,
char
direct
,
char
storev
,
lapack_int
m
,
lapack_int
n
,
lapack_int
k
,
const
double
*
v
,
lapack_int
ldv
,
const
double
*
t
,
lapack_int
ldt
,
double
*
c
,
lapack_int
ldc
);
lapack_int
LAPACKE_clarfb
(
int
matrix_layout
,
char
side
,
char
trans
,
char
direct
,
char
storev
,
lapack_int
m
,
lapack_int
n
,
lapack_int
k
,
const
lapack_complex_float
*
v
,
lapack_int
ldv
,
const
lapack_complex_float
*
t
,
lapack_int
ldt
,
lapack_complex_float
*
c
,
lapack_int
ldc
);
lapack_int
LAPACKE_zlarfb
(
int
matrix_layout
,
char
side
,
char
trans
,
char
direct
,
char
storev
,
lapack_int
m
,
lapack_int
n
,
lapack_int
k
,
const
lapack_complex_double
*
v
,
lapack_int
ldv
,
const
lapack_complex_double
*
t
,
lapack_int
ldt
,
lapack_complex_double
*
c
,
lapack_int
ldc
);
Include Files
  • mkl.h
Description
The real flavors of the routine
?larfb
 apply a real block reflector
H
 or its transpose
H
T
 to a real
m
-by-
n
 matrix
C
 from either left or right.
The complex flavors of the routine
?larfb
 apply a complex block reflector
H
 or its conjugate transpose
H
H
 to a complex
m
-by-
n
 matrix
C
 from either left or right.
Input Parameters
A
<datatype>
 placeholder, if present, is used for the C interface data types in the C interface section above. See C Interface Conventions for the C interface principal conventions and type definitions.
side
If
side
 =
'L'
: apply
H
 or
H
T
 for real flavors and
H
 or
H
H
 for complex flavors from the left.
If
side
 =
'R'
: apply
H
 or
H
T
 for real flavors and
H
 or
H
H
 for complex flavors from the right.
trans
If
trans
 =
'N'
: apply
H
 (No transpose).
If
trans
 =
'C'
: apply
H
H
 (Conjugate transpose).
If
trans
 =
'T'
: apply
H
T
 (Transpose).
direct
Indicates how
H
 is formed from a product of elementary reflectors
If
direct
 =
'F'
:
H
 =
H
(1)*H(2)*. . . *
H
(
k
)
 (forward)
If
direct
 =
'B'
:
H
 =
H
(
k
)* . . .
H
(2)*
H
(1)
 (backward)
storev
Indicates how the vectors which define the elementary reflectors are stored:
If
storev
 =
'C'
: Column-wise
If
storev
 =
'R'
: Row-wise
m
The number of rows of the matrix
C
.
n
The number of columns of the matrix
C
.
k
The order of the matrix
T
 (equal to the number of elementary reflectors whose product defines the block reflector).
v
The size limitations depend on values of parameters
storev
 and
side
 as described in the following table:
storev
 =
C
storev
 =
R
side
 =
L
side
 =
R
side
 =
L
side
 =
R
Column major
max(1,
ldv
*
k
)
max(1,
ldv
*
k
)
max(1,
ldv
*
m
)
max(1,
ldv
*
n
)
Row major
max(1,
ldv
*
m
)
max(1,
ldv
*
n
)
max(1,
ldv
*
k
)
max(1,
ldv
*
k
)
The matrix
v
.
See
Application Notes
 below.
ldv
The leading dimension of the array
v
.It should satisfy the following conditions:
storev
 =
C
storev
 =
R
side
 =
L
side
 =
R
side
 =
L
side
 =
R
Column major
max(1,
m
)
max(1,
n
)
max(1,
k
)
max(1,
k
)
Row major
max(1,
k
)
max(1,
k
)
max(1,
m
)
max(1,
n
)
t
Array, size
at least max(1,
ldt
 *
k
)
.
Contains the triangular
k
-by-
k
 matrix
T
 in the representation of the block reflector.
ldt
The leading dimension of the array
t
.
ldt
≥
k
.
c
Array, size
at least max(1,
ldc
 *
n
) for column major layout and max(1,
ldc
 *
m
) for row major layout
.
On entry, the
m
-by-
n
 matrix
C
.
ldc
The leading dimension of the array
c
.
ldc
≥
 max(1,
m
)
for column major layout and
ldc
≥
 max(1,
n
)
 for row major layout
.
Output Parameters
c
On exit,
c
 is overwritten by the product of the following:
  • H
    *
    C,
     or
    H
    T
    *
    C,
     or
    C
    *
    H,
     or
    C
    *
    H
    T
     for real flavors
  • H
    *
    C,
     or
    H
    H
    *
    C,
     or
    C
    *
    H,
     or
    C
    *
    H
    H
     for complex flavors
Return Values
This function returns a value
info
.
If
info
 = 0
, the execution is successful.
If
info
 =
-i
, the
i
-th parameter had an illegal value.
If
info
 = -1011
, memory allocation error occurred.
Application Notes
The shape of the matrix
V
 and the storage of the vectors which define the
H
(
i
) is best illustrated by the following example with
n
 = 5
 and
k
 = 3
. The elements equal to 1 are not stored; the corresponding array elements are modified but restored on exit. The rest of the array is not used.
Equation
Equation

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