1 #ifndef STAN_MATH_PRIM_FUN_COL_HPP
2 #define STAN_MATH_PRIM_FUN_COL_HPP
3 
4 #include <stan/math/prim/err.hpp>
5 #include <stan/math/prim/fun/Eigen.hpp>
6 
7 namespace stan {
8 namespace math {
9 
10 /**
11  * Return the specified column of the specified matrix
12  * using start-at-1 indexing.
13  *
14  * This is equivalent to calling <code>m.col(i - 1)</code> and
15  * assigning the resulting template expression to a column vector.
16  *
17  * @tparam T type of the matrix
18  * @param m Matrix.
19  * @param j Column index (count from 1).
20  * @return Specified column of the matrix.
21  * @throw std::out_of_range if j is out of range.
22  */
23 template <typename T, require_matrix_t<T>* = nullptr>
col(const T & m,size_t j)24 inline auto col(const T& m, size_t j) {
25   check_column_index("col", "j", m, j);
26   return m.col(j - 1);
27 }
28 
29 }  // namespace math
30 }  // namespace stan
31 
32 #endif
33