added subdomain support in Mesh class, CalculateLaplaceMult implementation

mgrid_2/geom.h

@@ -45,6 +45,16 @@ public:
     */
     explicit Mesh(std::string const &fname);
 
+    /**
+     * Reads mesh data plus subdomain data from a binary file.
+     *
+     * File format, see ascii_write_mesh.m
+     *
+     * @param[in] filename file name
+     * @param[in] subdomain_filename subdomain file name
+    */
+    explicit Mesh(std::string const &filename, std::string const &subdomain_filename);
+
     /**
      * Reads mesh data from a binary file.
      *
@@ -63,6 +73,8 @@ public:
         return _nelem;
     }
 
+    
+
     /**
      * Global number of vertices for each finite element.
      * @return number of vertices per element.
@@ -422,6 +434,7 @@ public:
      */
     void liftToQuadratic();    
 
+
 protected:
     //public:
     void SetNelem(int nelem)
@@ -522,7 +535,19 @@ public:
      */    
     [[nodiscard]] bool checkObtuseAngles() const;
 
-private:
+
+    std::vector<int> ElementSubdomains;
+
+    /**
+     * Reads the global triangle to subdomain mapping.
+     *
+     * @param[in] dname file name
+     *
+     * @see ascii_write_subdomains.m for the file format
+    */
+    [[nodiscard]] const std::vector<int> ReadElementSubdomains(std::string const &dname) const;
+
+
     /**
      * Calculates the largest inner angle in element @p idx.
      *