orgtr

Generates the real orthogonal matrix Q determined by sytrd. This routine belongs to the oneapi::mkl::lapacknamespace.

Syntax

void orgtr(cl::sycl::queue &queue, mkl::uplo uplo, std::int64_t n, cl::sycl::buffer<T> &a, std::int64_t lda, cl::sycl::buffer<T> &tau, cl::sycl::buffer<T> &scratchpad, std::int64_t scratchpad_size)

orgtr supports the following precisions and devices:

T

Devices supported

float

Host and CPU

double

Host and CPU

Description

The routine explicitly generates the n-by-n orthogonal matrix Q formed by sytrd when reducing a real symmetric matrix A to tridiagonal form: A = Q*T*QT. Use this routine after a call to sytrd.

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 sytrd function

n

The order of matrix Q (0≤n).

a

The buffer a returned by the sytrd function. The second dimension of a must be at least max(1, n).

lda

The leading dimension of a (n≤lda).

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 orgtr_scratchpad_size function.

Output Parameters

a

Overwritten by the orthogonal matrix Q.

Exceptions

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.