ungtr (USM Version)

oneMKL - Data Parallel C++ Developer Reference

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ID 772045

Date 11/07/2023

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ungtr (USM Version)

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

Description
API

Description

The routine explicitly generates the n-by-n unitary matrix Q formed by the hetrd (USM Version) when reducing a complex Hermitian matrix A to tridiagonal form: A = Q*T*QT. Use this routine after a call to hetrd (USM Version) function.

API

Syntax

namespace oneapi::mkl::lapack {
  sycl::event ungtr(sycl::queue &queue,
  mkl::uplo uplo,
  std::int64_t n,
  T *a,
  std::int64_t lda,
  T *tau,
  T *tau,
  T *scratchpad,
  std::int64_t scratchpad_size,
  const std::vector<sycl::event> &events = {})
}

ungtr (USM version) supports the following precision and devices.

T	Devices Supported
`float`	CPU
`double`	CPU

Input Parameters

queue: Device queue where calculations will be performed.
uplo: Must be uplo::upper or uplo::lower. Uses the same uplo as supplied to the hetrd (USM Version) function.
n: The order of matrix Q (0 ≤ n).
a: The pointer a returned by the hetrd (USM Version) function. The second dimension of a must be at least max(1, n).
lda: The leading dimension of a (lda ≥ n).
tau: The pointer tau returned by the hetrd (USM Version) function. The dimension of tau must be at least max(1,n-1).
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 ungtr_scratchpad_size function.
events: List of events to wait for before starting computation. Defaults to empty list.

Output Parameters

a: Overwritten by the 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.

Return Values

Output event to wait on to ensure computation is complete.

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oneMKL - Data Parallel C++ Developer Reference

ungtr (USM Version)

Description

API