csr_matrix_times_vector.hpp

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#ifndef STAN_MATH_PRIM_FUN_CSR_MATRIX_TIMES_VECTOR_HPP
#define STAN_MATH_PRIM_FUN_CSR_MATRIX_TIMES_VECTOR_HPP
 
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/csr_u_to_z.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/fun/dot_product.hpp>
#include <vector>
 
namespace stan {
namespace math {
 
template <typename T1, typename T2,
          require_all_not_rev_matrix_t<T1, T2>* = nullptr>
inline Eigen::Matrix<return_type_t<T1, T2>, Eigen::Dynamic, 1>
csr_matrix_times_vector(int m, int n, const T1& w, const std::vector<int>& v,
                        const std::vector<int>& u, const T2& b) {
  check_positive("csr_matrix_times_vector", "m", m);
  check_positive("csr_matrix_times_vector", "n", n);
  check_size_match("csr_matrix_times_vector", "n", n, "b", b.size());
  check_size_match("csr_matrix_times_vector", "w", w.size(), "v", v.size());
  check_size_match("csr_matrix_times_vector", "m", m, "u", u.size() - 1);
  check_size_match("csr_matrix_times_vector", "u/z",
                   u[m - 1] + csr_u_to_z(u, m - 1) - 1, "v", v.size());
  for (int i : v) {
    check_range("csr_matrix_times_vector", "v[]", n, i);
  }
  std::vector<int> v_zero_based(v.size());
  std::transform(v.begin(), v.end(), v_zero_based.begin(),
                 [](auto&& x) { return x - 1; });
  std::vector<int> u_zero_based(u.size());
  std::transform(u.begin(), u.end(), u_zero_based.begin(),
                 [](auto&& x) { return x - 1; });
  // u_zero_based[u.size()] = w.size();
  auto&& w_ref = to_ref(w);
  Eigen::Map<const Eigen::SparseMatrix<scalar_type_t<T1>, Eigen::RowMajor>>
      w_mat(m, n, w_ref.size(), u_zero_based.data(), v_zero_based.data(),
            w_ref.data());
  return w_mat * b;
}
 
}  // namespace math
}  // namespace stan
 
#endif