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 {
  sycl::event ungtr(sycl::queue &queue,
  mkl::uplo uplo,
  int64_t n,
  T *a,
  int64_t lda,
  const T *tau,
  T *scratchpad,
  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.

Return Values#

Output event to wait on to ensure computation is complete.