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 begenerate::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 matrixQorPTto 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 matrixQorPTto 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 leastmin(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 typeT. 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 matrixQorPT, (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. |