Contents

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

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 {
  cl::sycl::event ungtr(cl::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<cl::sycl::event> &events = {})
}

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

T

Devices Supported

float

Host and CPU

double

Host and 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 (n≤lda).

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.

Return Values

Output event to wait on to ensure computation is complete.

ungtr ungtr_scratchpad_size