added subdomain indexing for outer edges, for use in robin BC

mgrid_2/getmatrix.h

@@ -394,6 +394,20 @@ class FEM_Matrix: public CRS_Matrix
         */
        void ApplyDirichletBC(std::vector<double> const &u, std::vector<double> &f);
 
+        /**
+        * Applies Robin boundary conditions to stiffness matrix and to load vector @p f
+        * for multiple subdomains
+        * The <a href="https://www.jstor.org/stable/2005611?seq=1#metadata_info_tab_contents">penalty method</a>
+        * is used for incorporating the given values @p u.
+        *
+        * @param[in]     u (global) vector with Dirichlet data
+        * @param[in]     u_out outside temperature
+        * @param[in,out] f load vector
+        */
+       void ApplyRobinBC_mult(std::vector<double> const &u, std::vector<double> &f, const double u_out);
+
+       double Heat_transfer_coefficient(const int subdomain);
+
        /**
         * Extracts the diagonal elements of the sparse matrix.
         *