ungtr¶

Generates the complex unitary matrix Q determined by hetrd.

ungtr supports the following precisions.

T

std::complex<float>

std::complex<double>

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.

ungtr (BUFFER Version)¶

Syntax

void onemkl::lapack::ungtr(cl::sycl::queue &queue, onemkl::uplo upper_lower, std::int64_t n, cl::sycl::buffer<T, 1> &a, std::int64_t lda, cl::sycl::buffer<T, 1> &tau, cl::sycl::buffer<T, 1> &scratchpad, std::int64_t scratchpad_size)¶

Input Parameters

queue: The queue where the routine should be executed.
upper_lower: Must be uplo::upper or uplo::lower. Uses the same upper_lower as supplied to hetrd.
n: The order of the matrix Q(0≤n).
a: The buffer a as returned by hetrd. The second dimension of a must be at least max(1, n).
lda: The leading dimension of a(n≤lda).
tau: The buffer tau as returned by hetrd. The dimension of tau must be at least max(1, n-1).
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 ungtr_scratchpad_size function.

Output Parameters

a: Overwritten by the unitary matrix Q.
scratchpad: Buffer holding scratchpad memory to be used by routine for storing intermediate results.

Throws

onemkl::lapack::exception

Exception is thrown in case of problems happened during calculations. The info code of the problem can be obtained by get_info() method of exception object:

If info=-i, the i-th parameter had an illegal value.

If info equals to value passed as scratchpad size, and get_detail() returns non zero, then passed scratchpad is of insufficient size, and required size should not be less than value return by get_detail() method of exception object.

ungtr (USM Version)¶