cumulative_sum.hpp

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#ifndef STAN_MATH_PRIM_FUN_CUMULATIVE_SUM_HPP
#define STAN_MATH_PRIM_FUN_CUMULATIVE_SUM_HPP
 
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/meta.hpp>
#include <vector>
#include <numeric>
#include <functional>
 
namespace stan {
namespace math {
 
template <typename T>
inline std::vector<T> cumulative_sum(const std::vector<T>& x) {
  std::vector<T> result(x.size());
  if (x.size() == 0) {
    return result;
  }
  std::partial_sum(x.begin(), x.end(), result.begin(), std::plus<T>());
  return result;
}
 
template <typename EigVec, require_eigen_vector_t<EigVec>* = nullptr,
          require_not_st_var<EigVec>* = nullptr>
inline auto cumulative_sum(const EigVec& m) {
  using T_scalar = value_type_t<EigVec>;
  Eigen::Matrix<T_scalar, EigVec::RowsAtCompileTime, EigVec::ColsAtCompileTime>
      result(m.rows(), m.cols());
  if (m.size() == 0) {
    return result;
  }
  const auto& m_ref = to_ref(m);
  result.coeffRef(0) = m_ref.coeff(0);
  for (Eigen::Index i = 1; i < m_ref.size(); ++i) {
    result.coeffRef(i) = m_ref.coeff(i) + result.coeffRef(i - 1);
  }
  return result;
}
 
}  // namespace math
}  // namespace stan
 
#endif