ungtr

oneMKL - Data Parallel C++ Developer Reference

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ID 772045

Date 6/24/2024

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ungtr

Generates the complex unitary matrix Q determined by hetrd. 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 hetrd when reducing a complex Hermitian matrix A to tridiagonal form: A = Q*T*QH. Use this routine after a call to hetrd.

API

Syntax

namespace oneapi::mkl::lapack {
  void ungtr(sycl::queue &queue,
  mkl::uplo uplo,
  std::int64_t n,
  sycl::buffer<T> &a,
  std::int64_t lda,
  sycl::buffer<T> &tau,
  sycl::buffer<T> &scratchpad,
  std::int64_t scratchpad_size)
}

ungtr supports the following precision and devices.

T	Devices Supported
`std::complex<float>`	CPU
`std::complex<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 function.
n: The order of matrix Q (0 ≤ n).
a: The buffer a returned by the hetrd function. The second dimension of a must be at least max(1, n).
lda: The leading dimension of a (lda ≥ n).
tau: The buffer tau returned by the hetrd function. The dimension of tau must be at least max(1,n-1).
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 ungtr_scratchpad_size function.

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.

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oneMKL - Data Parallel C++ Developer Reference

ungtr

Description

API