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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>

Note

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.

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