ungqr

oneMKL - Data Parallel C++ Developer Reference

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ID 772045

Date 11/07/2023

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ungqr

Generates the complex unitary matrix Q of the QR factorization formed by geqrf. This routine belongs to the oneapi::mkl::lapack namespace.

Description
API

Description

The routine generates the whole or part of m-by-m unitary matrix Q of the QR factorization formed by the routines geqrf.

Usually Q is determined from the QR factorization of an m by p matrix A with m ≥ p. To compute the whole matrix Q, use:

mkl::ungqr(queue, m, m, p, a, lda, tau, ...)

To compute the leading p columns of Q (which form an orthonormal basis in the space spanned by the columns of A):

mkl::ungqr(queue, m, p, p, a, lda, tau, ...)

To compute the matrix Q^k of the QR factorization of the leading k columns of the matrix A:

mkl::ungqr(queue, m, m, k, a, lda, tau, ...)

To compute the leading k columns of Q^k (which form an orthonormal basis in the space spanned by the leading k columns of the matrix A):

mkl::ungqr(queue, m, k, k, a, lda, tau, ...)

API

Syntax

namespace oneapi::mkl::lapack {
  void ungqr(sycl::queue &queue,
  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)
}

ungqr`` supports the following precisions and devices:

T	Devices supported
`std::complex<float>`	CPU and GPU*
`std::complex<double>`	CPU and GPU*

*Interface support only; all computations are performed on the CPU.

Input Parameters

queue: Device queue where calculations will be performed.
m: The number of rows in the matrix A (0 ≤ m).
n: The number of columns in the matrix A (0 ≤ n).
k: The number of elementary reflectors whose product defines the matrix Q (0 ≤ k ≤ n).
a: Buffer holding the result of geqrf.
lda: The leading dimension of A (lda ≥ m).
tau: Buffer holding the result of geqrf.
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 ungqr_scratchpad_size function.

Output Parameters

a: Overwritten by n leading columns of the m-by-m unitary matrix Q.

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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ungqr

Description

API