Developer Reference

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ungbr

Generates the complex unitary matrix Q or P
t
determined by gebrd. This routine belongs to the
oneapi::mkl::lapack
namespace.

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:
ungbr(queue, generate::q, m, m, n, a, ...)
(note that the buffer
a
must have at least
m
columns).
To form the
n
leading columns of
Q
if
m > n
, use:
ungbr(queue, generate::q, m, n, n, a, ...)
To compute the whole
n
-by-
n
matrix
P
T
, use:
ungbr(queue, generate::p, n, n, m, a, ...)
(note that the array
a
must have at least
n
rows).
To form the
m
leading rows of
P
T
if
m < n
, use:
ungbr(queue, generate::p, m, n, m, a, ...)

API

Syntax
namespace oneapi::mkl::lapack { void ungbr(cl::sycl::queue &queue, mkl::generate gen, std::int64_t m, std::int64_t n, std::int64_t k, cl::sycl::buffer<T> &a, std::int64_t lda, cl::sycl::buffer<T> &tau, cl::sycl::buffer<T> &scratchpad, std::int64_t scratchpad_size) }
ungbr
supports the following precisions and devices:
T
Devices supported
std::complex<float>
Host and CPU
std::complex<double>
Host and CPU
Input Parameters
queue
Device queue where calculations will be performed.
gen
Must be
generate::q
or
generate::p
.
If gen
= generate::q
, the routine generates the matrix
Q
.
If gen
= generate::p
, the routine generates the matrix
P
T
.
m
The number of rows in the matrix
Q
or
P
T
to be returned
(0≤m)
.
If gen
= generate::q
,
m ≥ n ≥ min(m, k)
.
If gen
= generate::p
,
n ≥ m ≥ min(n, k)
.
n
The number of rows in the matrix
Q
or
P
T
to be returned
(0≤n)
. See m for constraints.
k
If gen
= generate::q
, the number of columns in the original
m
-by-k matrix reduced by gebrd.
If gen
= generate::p
, the number of rows in the original
k
-by-n matrix reduced by gebrd.
a
Buffer holding memory returned by gebrd.
lda
The leading dimension of a.
tau
For gen
= generate::q
, the array tauq is returned by the gebrd function.
For gen
= generate::p
, the array taup is returned by the gebrd function.
The dimension of tau must be at least
min(m,k)
for
gen = generate::q
, or
min(n,k)
for
gen = generate::p
.
scratchpad
Buffer holding scratchpad memory to be used by the routine for storing intermediate results.
scratchpad_size
Size of scratchpad memory as a number of floating point elements of type
T
. Size should not be less than the value returned by the ungbr_scratchpad_size function.
Output Parameters
a
Overwritten by n leading columns of the m-by-m unitary matrix
Q
or
P
T
, (or the leading rows or columns thereof) as specified by gen, m, and n.
Exceptions
Exception
Description
mkl::lapack::exception
This exception is thrown when problems occur during calculations. You can obtain the info code of the problem using the info() method of the exception object:
If
info = -i
, the
i
-th parameter had an illegal value.
If
info
is equal to the value passed as scratchpad size, and detail() returns non-zero, then the passed scratchpad has an insufficient size, and the required size should not be less than the value returned by the detail() method of the exception object.

Product and Performance Information

1

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