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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).

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 supports the following precisions.

T

float

double

std::complex<float>

std:complex<double>

Note

The index is zero-based.

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

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. The buffer must be of size 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.

Throws

This routine shall throw the following exceptions if the associated condition is detected. An implementation may throw additional implementation-specific exception(s) in case of error conditions not covered here.

oneapi::mkl::invalid_argument

oneapi::mkl::unsupported_device

oneapi::mkl::host_bad_alloc

oneapi::mkl::device_bad_alloc

oneapi::mkl::unimplemented

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 the input vector x. The array holding the input vector x must be of size 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.

Throws

This routine shall throw the following exceptions if the associated condition is detected. An implementation may throw additional implementation-specific exception(s) in case of error conditions not covered here.

oneapi::mkl::invalid_argument

oneapi::mkl::unsupported_device

oneapi::mkl::host_bad_alloc

oneapi::mkl::device_bad_alloc

oneapi::mkl::unimplemented

Parent topic: BLAS Level 1 Routines

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