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ungbr (USM Version)

Generates the complex unitary matrix Q or Pt determined by the gebrd (USM Version) function. This routine belongs to the oneapi::mkl::lapack namespace.

Description

The routine generates the whole or part of the unitary matrices Q and PT formed by the gebrd (USM Version) function. 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 array 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 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 {
  cl::sycl::event ungbr(cl::sycl::queue &queue,
  mkl::generate gen,
  std::int64_t m,
  std::int64_t n,
  std::int64_t k,
  T *a,
  std::int64_t lda,
  T *tau,
  T *scratchpad,
  std::int64_t scratchpad_size,
  const std::vector<cl::sycl::event> &events = {})
}

ungbr (USM version) 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 PT.

m

The number of rows in the matrix Q or PT 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 PT 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 (USM Version).

If gen= generate::p, the number of rows in the original k-by-n matrix reduced by gebrd (USM Version).

a

Pointer to memory returned by gebrd (USM Version).

lda

The leading dimension of a.

tau

For gen= generate::q, the array tauq is returned by the gebrd (USM Version) function.

For gen= generate::p, the array taup is returned by the gebrd (USM Version) 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

Pointer to 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.

events

List of events to wait for before starting computation. Defaults to empty list.

Output Parameters

a

Overwritten by n leading columns of the m-by-m orthogonal matrix Q or PT (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.

Return Values

Output event to wait on to ensure computation is complete.

ungbr ungbr_scratchpad_size