Developer Reference for Intel® oneAPI Math Kernel Library - C

Developer Reference

Contents

?ungbr

Generates the complex unitary matrix Q or
P
H
 determined by
?gebrd
.

Syntax

lapack_int
LAPACKE_cungbr
(
int
matrix_layout
,
char
vect
,
lapack_int
m
,
lapack_int
n
,
lapack_int
k
,
lapack_complex_float
*
a
,
lapack_int
lda
,
const
lapack_complex_float
*
tau
);
lapack_int
LAPACKE_zungbr
(
int
matrix_layout
,
char
vect
,
lapack_int
m
,
lapack_int
n
,
lapack_int
k
,
lapack_complex_double
*
a
,
lapack_int
lda
,
const
lapack_complex_double
*
tau
);
Include Files
  • mkl.h
Description
The routine generates the whole or part of the unitary matrices
Q
 and
P
H
 formed by the routines gebrd. Use this routine after a call to
cgebrd
/
zgebrd
. All valid combinations of arguments are described in
Input Parameters
; in most cases you need the following:
To compute the whole
m
-by-
m
 matrix
Q
, use:
LAPACKE_?ungbr(matrix_layout, 'Q', m, m, n, a, lda, tau)
(note that the
array
a
 must have at least
m
 columns).
To form the
n
 leading columns of
Q
 if
m
 >
n
, use:
LAPACKE_?ungbr(matrix_layout, 'Q', m, n, n, a, lda, tau)
To compute the whole
n
-by-
n
 matrix
P
H
, use:
LAPACKE_?ungbr(matrix_layout, 'P', n, n, m, a, lda, tau)
(note that the array
a
 must have at least
n
 rows).
To form the
m
 leading rows of
P
H
 if
m
 <
n
, use:
LAPACKE_?ungbr(matrix_layout, 'P', m, m, n, a, lda, tau)
Input Parameters
matrix_layout
Specifies whether matrix storage layout is row major (
LAPACK_ROW_MAJOR
) or column major (
LAPACK_COL_MAJOR
).
vect
Must be
'Q'
 or
'P'
.
If
vect
 =
'Q'
, the routine generates the matrix
Q
.
If
vect
 =
'P'
, the routine generates the matrix
P
H
.
m
The number of required rows of
Q
 or
P
H
.
n
The number of required columns of
Q
 or
P
H
.
k
One of the dimensions of
A
 in
?gebrd
:
If
vect
 =
'Q'
, the number of columns in
A
;
If
vect
 =
'P'
, the number of rows in
A
.
Constraints:
m
≥
 0
,
n
≥
 0
,
k
≥
 0
.
For
vect
 =
'Q'
:
k
≤
n
≤
m
 if
m
 >
k
, or
m
 =
n
 if
m
≤
k
.
For
vect
 =
'P'
:
k
≤
m
≤
n
 if
n
 >
k
, or
m
 =
n
 if
n
≤
k
.
a
Arrays:
a
, size at least
lda
*
n
 for column major layout and
lda
*
m
 for row major layout,
 is the array
a
 as returned by
?gebrd
.
lda
The leading dimension of
a
; at least max(1,
m
)
for column major layout and max(1,
n
) for row major layout
.
tau
For
vect
 =
'Q'
, the array
tauq
 as returned by
?gebrd
. For
vect
 =
'P'
, the array
taup
 as returned by
?gebrd
.
The dimension of
tau
 must be at least max(1, min(
m
,
k
)) for
vect
 =
'Q'
, or max(1, min(
m
,
k
)) for
vect
 =
'P'
.
Output Parameters
a
Overwritten by the orthogonal matrix
Q
 or
P
T
 (or the leading rows or columns thereof) as specified by
vect
,
m
, and
n
.
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.
Application Notes
The computed matrix
Q
 differs from an exactly orthogonal matrix by a matrix
E
 such that
||
E
||
2
 =
O
(
ε
)
.
The approximate numbers of possible floating-point operations are listed below:
To compute the whole matrix
Q
:
(16/3)
n
(3
m
2
 - 3
m
*
n
 +
n
2
)
 if
m
 >
n
;
(16/3)
m
3
 if
m
≤
n
.
To form the
n
 leading columns of
Q
 when
m
 >
n
:
(8/3)
n
2
(3
m
 -
n
2
)
.
To compute the whole matrix
P
H
:
(16/3)
n
3
 if
m
≥
n
;
(16/3)
m
(3
n
2
 - 3
m
*
n
 +
m
2
)
 if
m
 <
n
.
To form the
m
 leading columns of
P
H
 when
m
 <
n
:
(8/3)
n
2
(3
m
 -
n
2
)
 if
m
 >
n
.
The real counterpart of this routine is orgbr.

Product and Performance Information

1

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