Developer Reference

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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.

Product and Performance Information

1

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