Function b_ref

cpp/demo/custom_kernel/main.cpp:56–63

/// @return RHS reference vector.
template <typename T>
std::array<T, 3> b_ref(mdspand_t<const T, 4> phi, std::span<const T> w)
{
  std::array<T, 3> b{};
  for (std::size_t k = 0; k < phi.extent(1); ++k) // quadrature point
    for (std::size_t i = 0; i < b.size(); ++i)    // row i
      b[i] += w[k] * phi(0, k, i, 0);
  return b;
}

/// @brief Assemble a matrix operator using a `std::function` kernel
/// function.