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

Developer Reference

Contents

geqrf (USM Version)

Computes the QR factorization of a general m-by-n matrix. This routine belongs to the
oneapi::mkl::lapack
 namespace.

Description

The routine forms the
QR
 factorization of a general
m
-by-
n
 matrix
A
. No pivoting is performed.
The routine does not form the matrix
Q
 explicitly. Instead,
Q
 is represented as a product of min(
m
,
n
) elementary reflectors. Routines are provided to work with
Q
 in this representation.

API

Syntax
namespace oneapi::mkl::lapack {
   cl::sycl::event geqrf(cl::sycl::queue &queue,
   std::int64_t m,
   std::int64_t n,
   T *a,
   std::int64_t lda,
   T *tau,
   T *scratchpad,
   std::int64_t scratchpad_size,
   const std::vector<cl::sycl::event> &events = {})
}
gerqf
 (USM version) supports the following precisions and devices:
T
Devices supported
float
Host, CPU, and GPU
double
Host, CPU, and GPU
std::complex<float>
Host, CPU, and GPU
std::complex<double>
Host, CPU, and GPU
Input Parameters
queue
Device queue where calculations will be performed.
m
The number of rows in the matrix
A
 (
0≤m
).
n
The number of columns in the matrix
A
 (
0≤n
).
a
Pointer to the memory holding input matrix
A
. The second dimension of
a
 must be at least
max(1, n)
.
lda
The leading dimension of
a
, at least
max(1, m)
.
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 geqrf_scratchpad_size function.
events
List of events to wait for before starting computation. Defaults to empty list.
Output Parameters
a
Overwritten by the factorization data as follows:
The elements on and above the diagonal of the array contain the
min(m,n)
-by-
n
 upper trapezoidal matrix
R
 (
R
 is upper triangular if
m≥n
); the elements below the diagonal, with the array tau, present the orthogonal matrix
Q
 as a product of
min(m,n)
 elementary reflectors.
tau
Array, size at least
min(m,n)
.
Contains scalars that define elementary reflectors for the matrix
Q
 in its decomposition in a product of elementary reflectors.
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.