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 |
---|
|
|
|
|
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<std::int64_t, 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<std::int64_t, 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:
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,
std::int64_t *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,
std::int64_t *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 vectorx
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.