csr_to_dense_matrix.hpp

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#ifndef STAN_MATH_PRIM_FUN_CSR_TO_DENSE_MATRIX_HPP
#define STAN_MATH_PRIM_FUN_CSR_TO_DENSE_MATRIX_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/to_ref.hpp>
#include <vector>
 
namespace stan {
namespace math {
 
template <typename T>
inline Eigen::Matrix<value_type_t<T>, Eigen::Dynamic, Eigen::Dynamic>
csr_to_dense_matrix(int m, int n, const T& w, const std::vector<int>& v,
                    const std::vector<int>& u) {
  using Eigen::Dynamic;
  using Eigen::Matrix;
 
  check_positive("csr_to_dense_matrix", "m", m);
  check_positive("csr_to_dense_matrix", "n", n);
  check_size_match("csr_to_dense_matrix", "m", m, "u", u.size() - 1);
  check_size_match("csr_to_dense_matrix", "w", w.size(), "v", v.size());
  check_size_match("csr_to_dense_matrix", "u/z",
                   u[m - 1] + csr_u_to_z(u, m - 1) - 1, "v", v.size());
  for (int i : v) {
    check_range("csr_to_dense_matrix", "v[]", n, i);
  }
  const auto& w_ref = to_ref(w);
  Matrix<value_type_t<T>, Dynamic, Dynamic> result(m, n);
  result.setZero();
  for (int row = 0; row < m; ++row) {
    int row_nnz = csr_u_to_z(u, row);
 
    if (row_nnz > 0) {
      int row_end_in_w = (u[row] - stan::error_index::value) + row_nnz;
      check_range("csr_to_dense_matrix", "w", w.size(), row_end_in_w);
      for (int nze = u[row] - stan::error_index::value; nze < row_end_in_w;
           ++nze) {
        // row is row index, v[nze] is column index. w[nze] is entry value.
        check_range("csr_to_dense_matrix", "j", n, v[nze]);
        result(row, v[nze] - stan::error_index::value) = w_ref.coeff(nze);
      }
    }
  }
  return result;
}  // end of csr_format group
 
}  // namespace math
}  // namespace stan
 
#endif