ungbr

oneMKL - Data Parallel C++ Developer Reference

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ID 772045

Date 7/13/2023

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ungbr

Generates the complex unitary 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 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 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 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(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)
}

ungbr supports the following precisions and devices:

T	Devices supported
`std::complex<float>`	CPU
`std::complex<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

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) for gen = generate::q, or min(n,k) for gen = 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 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

ungbr

Description

API