1 #ifndef STAN_MATH_PRIM_FUN_CROSSPROD_HPP
2 #define STAN_MATH_PRIM_FUN_CROSSPROD_HPP
3 
4 #include <stan/math/prim/meta.hpp>
5 #include <stan/math/prim/fun/typedefs.hpp>
6 #include <stan/math/prim/fun/tcrossprod.hpp>
7 
8 namespace stan {
9 namespace math {
10 
11 /**
12  * Returns the result of pre-multiplying a matrix by its
13  * own transpose.
14  *
15  * @tparam EigMat type of the matrix (must be derived from \c Eigen::MatrixBase)
16  * @param M Matrix to multiply.
17  * @return Transpose of M times M
18  */
19 template <typename EigMat, require_eigen_t<EigMat>* = nullptr>
crossprod(const EigMat & M)20 inline auto crossprod(const EigMat& M) {
21   return tcrossprod(M.transpose());
22 }
23 
24 }  // namespace math
25 }  // namespace stan
26 
27 #endif
28