orgbr

oneMKL - Data Parallel C++ Developer Reference

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ID 772045

Date 3/31/2021

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orgbr

Generates the real orthogonal matrix Q or P^T determined by gebrd. This routine belongs to the oneapi::mkl::lapack namespace.

Description
API

Description

The routine generates the whole or part of the orthogonal matrices Q and P^T formed by the routines gebrd. Use this routine after a call to sgebrd/dgebrd. 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:

orgbr(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:

orgbr(queue, generate::q, m, n, n, a, ...)

To compute the whole n-by-n matrix P^T:

orgbr(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:

orgbr(queue, generate::p, m, n, m, a, ...)

API

Syntax

namespace oneapi::mkl::lapack {
  void orgbr(sycl::queue &queue,
  mkl::generate gen,
  std::int64_t m,
  std::int64_t n,
  std::int64_t k,
  sycl::buffer<T> &a,
  std::int64_t lda,
  sycl::buffer<T> &tau,
  sycl::buffer<T> &scratchpad,
  std::int64_t scratchpad_size)
}

orgbr supports the following precisions and devices:

T	Devices supported
`float`	CPU
`double`	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

Buffer holding array of size min (m,k) if gen= generate::q, and of size min(n,k) if gen= generate::p. Scalar factor of the elementary reflectors, as returned by gebrd in the array tauq or taup.

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 orgbr_scratchpad_size function.

Output Parameters

a: Overwritten by n leading columns of the m-by-m orthogonal 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.

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.

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oneMKL - Data Parallel C++ Developer Reference

orgbr

Description

API