--- a
+++ b/src/eigen.cc
@@ -0,0 +1,38 @@
+//=============================================================================
+//
+// Copyright (c) 2020 Marco Colombo
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+//=============================================================================
+
+#include <RcppEigen.h>
+
+// [[Rcpp::export]]
+Eigen::MatrixXd multiplyAB(const Eigen::Map<Eigen::MatrixXd>& A,
+                           const Eigen::Map<Eigen::MatrixXd>& B) {
+  return A * B;
+}
+
+// [[Rcpp::export]]
+Eigen::MatrixXd multiplyAtB(const Eigen::Map<Eigen::MatrixXd>& A,
+                            const Eigen::Map<Eigen::MatrixXd>& B) {
+  return A.transpose() * B;
+}
+
+// [[Rcpp::export]]
+Eigen::MatrixXd multiplyABt(const Eigen::Map<Eigen::MatrixXd>& A,
+                            const Eigen::Map<Eigen::MatrixXd>& B) {
+  return A * B.transpose();
+}