Contents

?geqrt2

Computes a QR factorization of a general real or complex matrix using the compact WY representation of Q.

Syntax

Include Files
• mkl.h
Description
The strictly lower triangular matrix
V
contains the elementary reflectors
H
(
i
) in the
i
th column below the diagonal. For example, if
m
=5 and
n
=3, the matrix
V
is
where
v
i
represents the vector that defines
H
(
i
). The vectors are returned in the lower triangular part of array
a
.
The 1s along the diagonal of
V
are not stored in
a
.
The block reflector
H
is then given by
H
=
I
-
V
*
T
*
V
T
for real flavors, and
H
=
I
-
V
*
T
*
V
H
for complex flavors,
where
V
T
is the transpose and
V
H
is the conjugate transpose of
V
.
Input Parameters
m
The number of rows in the matrix
A
(
m
n
).
n
The number of columns in
A
(
n
≥ 0).
a
Array, size
at least
max(1,
lda
*
n
)
for column major and
max(1,
lda
*
m
)
for row major layout
. Array
a
contains the
m
-by-
n
matrix
A
.
lda
a
; at least max(1,
m
)
for column major layout and max(1,
n
) for row major layout
.
ldt
t
; at least max(1,
n
).
Output Parameters
a
Overwritten by the factorization data as follows:
The elements on and above the diagonal of the array contain the
n
-by-
n
upper triangular matrix
R
. The elements below the diagonal are the columns of
V
.
t
Array, size
at least
max(1,
ldt
*
n
)
.
The
n
-by-
n
upper triangular factor of the block reflector. The elements on and above the diagonal contain the block reflector
T
. The elements below the diagonal are not used.
Return Values
This function returns a value
info
.
If
info
= 0, the execution is successful.
If
info
< 0 and
info
=
-i
, the
i
th argument had an illegal value.
If
info
= -1011
, memory allocation error occurred.

Product and Performance Information

1

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