Function A_ref

cpp/demo/custom_kernel/main.cpp:39–48

/// @return Element reference matrix (row-major storage).
template <typename T>
std::array<T, 9> A_ref(mdspand_t<const T, 4> phi, std::span<const T> w)
{
  std::array<T, 9> A_b{};
  mdspan2_t<T, 3, 3> A(A_b.data());
  for (std::size_t k = 0; k < phi.extent(1); ++k)   // quadrature point
    for (std::size_t i = 0; i < A.extent(0); ++i)   // row i
      for (std::size_t j = 0; j < A.extent(1); ++j) // column j
        A(i, j) += w[k] * phi(0, k, i, 0) * phi(0, k, j, 0);
  return A_b;
}

/// @brief Compute the P1 RHS vector for f=1 on the reference cell.
/// @tparam T Scalar type.