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iamax

Finds the index of the element with the largest absolute value in a vector.

Description

The
iamax
routines return an index
i
such that
x[i]
has the maximum absolute value of all elements in vector
x
(real variants), or such that (|Re(
x[i]
)| + |Im(
x[i]
)|) is maximal (complex variants).
iamax
supports the following precisions:
T
float
double
std::complex<float>
std:complex<double>
The index is zero-based.
If either
n
or
incx
are not positive, the routine returns
0
.
If more than one vector element is found with the same largest absolute value, the index of the first one encountered is returned.
If the vector contains
NaN
values, then the routine returns the index of the first
NaN
.

iamax (Buffer Version)

Syntax
namespace oneapi::mkl::blas::column_major { void iamax(sycl::queue &queue, std::int64_t n, sycl::buffer<T, 1> &x, std::int64_t incx, sycl::buffer<std::int64_t, 1> &result) }
namespace oneapi::mkl::blas::row_major { void iamax(sycl::queue &queue, std::int64_t n, sycl::buffer<T, 1> &x, std::int64_t incx, sycl::buffer<std::int64_t, 1> &result) }
Input Parameters
exec_queue
The queue where the routine should be executed.
n
The number of elements in vector
x
.
x
The buffer that holds the input vector
x
. Size of the buffer must be at least (1 + (
n
- 1)*abs(
incx
)). See Matrix Storage for more details.
incx
The stride of vector
x
.
Output Parameters
result
The buffer where the zero-based index
i
of the maximal element is stored.

Examples

An example of how to use
iamax
can be found in the oneMKL installation directory, under:
examples/dpcpp/blas/source/iamax.cpp

iamax (USM Version)

Syntax
namespace oneapi::mkl::blas::column_major { sycl::event iamax(sycl::queue &queue, std::int64_t n, const T *x, std::int64_t incx, T_res *result, const std::vector<sycl::event> &dependencies = {}) }
namespace oneapi::mkl::blas::row_major { sycl::event iamax(sycl::queue &queue, std::int64_t n, const T *x, std::int64_t incx, T_res *result, const std::vector<sycl::event> &dependencies = {}) }
Input Parameters
queue
The queue where the routine should be executed.
n
The number of elements in vector
x
.
x
The pointer to input vector
x
. Size of the array holding input vector
x
must be at least (1 + (
n
- 1)*abs(
incx
)). See Matrix Storage for more details.
incx
The stride of vector
x
.
dependencies
List of events to wait for before starting computation, if any. If omitted, defaults to no dependencies.
Output Parameters
result
The pointer to where the zero-based index
i
of the maximal element is stored.
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.