KokkosBlas::gemv

Defined in header: KokkosBlas2_gemv.hpp

template <class ExecutionSpace, class AViewType, class XViewType, class YViewType>
void gemv(const ExecutionSpace& space, const char trans[], typename AViewType::const_value_type& alpha,
          const AViewType& A, const XViewType& x, typename YViewType::const_value_type& beta, const YViewType& y);

template <class AViewType, class XViewType, class YViewType>
void gemv(const char trans[], typename AViewType::const_value_type& alpha, const AViewType& A, const XViewType& x,
          typename YViewType::const_value_type& beta, const YViewType& y);

Perform a dense matrix-vector multiplication

\[y = \beta * y + \alpha * A * x\]

  1. Iterate over the entries of y, scale them with beta, compute the dot product of the corresponding row of A with x, scale it with alpha and accumulate to y using resources from the space instance, or

  2. Iterate over the entries of y, scale them with beta, compute the dot product of the corresponding row of A with x, scale it with alpha and accumulate to y using resources from the default instance of typename AViewType::execution_space.

The function will throw a runtime exception if any of the following conditions are not met:

  • trans stores a valid control value, see below

  • trans == N && A.extent(1) == x.extent(0) && A.extent(0) == y.extent(0)

  • trans == T,C && A.extent(0) == x.extent(0) && A.extent(1) == y.extent(0)

Parameters

space:

execution space instance.

trans:

“N” for no transpose, “T” for transpose and “C” for conjugate transpose of A, all characters after the first one are ignored.

alpha, beta:

scaling parameters for A*x and y, respectively.

A:

matrix being multiplied with x.

x, y:

input and output vectors for the matrix-vector multiplication, respectively.

Type Requirements

  • execution_space must be a Kokkos execution space

  • AViewType must be a Kokkos View of rank 2 that satisfies

    • Kokkos::SpaceAccessibility<ExecutionSpace, typename AViewType::memory_space>::accessible

  • XViewType must be a Kokkos View of rank 1 that satisfies

    • Kokkos::SpaceAccessibility<ExecutionSpace, typename XViewType::memory_space>::accessible

  • YViewType must be a Kokkos View of rank 1 that satisfies

    • Kokkos::SpaceAccessibility<ExecutionSpace, typename YViewType::memory_space>::accessible

Example

#include<Kokkos_Core.hpp>
#include<KokkosBlas2_gemv.hpp>

int main(int argc, char* argv[]) {
  Kokkos::initialize();
  {
    int M = atoi(argv[1]);
    int N = atoi(argv[2]);

    Kokkos::View<double**> A("A",M,N);
    Kokkos::View<double*> x("X",N);
    Kokkos::View<double*> y("Y",N);

    Kokkos::deep_copy(A,1.0);
    Kokkos::deep_copy(x,3.0);

    const double alpha = double(1.0);
    const double beta = double(0.0);

    KokkosBlas::gemv("N",alpha,A,x,beta,y);
  }
  Kokkos::finalize();
}