Intel® oneAPI Math Kernel Library (oneMKL) - Data Parallel C++ Developer Reference

Developer Reference

Contents

ungtr

Generates the complex unitary matrix Q determined by hetrd. This routine belongs to the
oneapi::mkl::lapack
 namespace.

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(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)
}
ungtr
 supports the following precision and devices.
T
Devices Supported
std::complex<float>
Host and CPU
std::complex<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 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
 (
n≤lda
).
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.

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.