iamax

oneMKL - Data Parallel C++ Developer Reference

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ID 772045

Date 3/22/2024

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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 a result type Tresult of std::int32_t or std::int64_t and support the following precisions for the data type T:

T
`float`
`double`
`std::complex<float>`
`std::complex<double>`

NOTE:

The index is zero-based if base is set to index_base::zero (default) or one-based if it is set to index_base::one.

If either n or incx is not positive, the routine returns 0, regardless of the base of the index selected.

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<Tresult, 1> &result,
               index_base base = index_base::zero)
}

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<Tresult, 1> &result,
               index_base base = index_base::zero)
}

Input Parameters

queue

The queue where the routine will 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.

base

Indicates how the output value is indexed. If omitted, defaults to zero-based indexing.

`oneapi::mkl::index_base::zero`	Zero-based (C-style) indexing: indices start at 0.
`oneapi::mkl::index_base::one`	One-based (Fortran-style) indexing: indices start at 1.

Output Parameters

result: The buffer where the 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:

share/doc/mkl/examples/sycl/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,
                      Tresult *result,
                      index_base base = index_base::zero,
                      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,
                      Tresult *result,
                      index_base base = index_base::zero,
                      const std::vector<sycl::event> &dependencies = {})
}

Input Parameters

queue

The queue where the routine will 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.

base

Indicates how the output value is indexed. If omitted, defaults to zero-based indexing.

`oneapi::mkl::index_base::zero`	Zero-based (C-style) indexing: indices start at 0.
`oneapi::mkl::index_base::one`	One-based (Fortran-style) indexing: indices start at 1.

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 index i of the maximal element is stored.

Return Values

Output event to wait on to ensure computation is complete.

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oneMKL - Data Parallel C++ Developer Reference

iamax

Description

iamax (Buffer Version)

Examples

iamax (USM Version)