ungbr#
Generates the complex unitary matrix Q or Pt 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 PH 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 buffera 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 PT, 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 PT if m < n, use:
ungbr(queue, generate::p, m, n, m, a, ...)
API#
Syntax#
namespace oneapi::mkl::lapack {
void ungbr(sycl::queue &queue,
mkl::generate gen,
int64_t m,
int64_t n,
int64_t k,
sycl::buffer<T> &a,
int64_t lda,
sycl::buffer<T> &tau,
sycl::buffer<T> &scratchpad,
int64_t scratchpad_size)
}
ungbr supports the following precisions and devices:
T |
Devices supported |
|---|---|
|
CPU |
|
CPU |
Input Parameters#
- queue
Device queue where calculations will be performed.
- gen
Must be
generate::qorgenerate::p.If gen
= generate::q, the routine generates the matrixQ.If gen
= generate::p, the routine generates the matrixPT.- m
The number of rows in the matrix
QorPT 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
QorPT to be returned(0 ≤ n). See m for constraints.- k
If gen
= generate::q, the number of columns in the originalm-by-k matrix reduced by gebrd.If gen
= generate::p, the number of rows in the originalk-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)forgen = generate::q, ormin(n,k)forgen = 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
QorPT, (or the leading rows or columns thereof) as specified by gen, m, and n.
Exceptions#
Exception |
Description |
|---|---|
|
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 If |