--- a/+multiblock/Grid.m	Wed Aug 02 19:26:39 2017 +0200
+++ b/+multiblock/Grid.m	Mon Aug 07 09:56:01 2017 +0200
@@ -9,16 +9,19 @@
 
     % General multiblock grid
     methods
-
-        % grids -- cell array of N grids
-        % connections -- NxN upper triangular cell matrix. connections{i,j}
-        %                specifies the connection between block i and j. If
-        %                it's empty there is no connection otherwise it's a 2
-        %                -cell-vector with strings naming the boundaries to be
-        %                connected. (inverted coupling?)
-        %% Should we have boundary groups at all? maybe it can be handled in a
-        %% cleaner way outside of the class. Maybe the grid class doesn't need to care at all. All boundaryGroup interaction is in DiffOp?
+        % grids          -- cell array of N grids
+        % connections    -- NxN upper triangular cell matrix. connections{i,j}
+        %                   specifies the connection between block i and j. If
+        %                   it's empty there is no connection otherwise it's a 2
+        %                   -cell-vector with strings naming the boundaries to be
+        %                   connected. (inverted coupling?)
+        % boundaryGroups -- A struct of BoundaryGroups. The field names of the
+        %                   struct are the names of each boundary group.
+        %                   The boundary groups can be used to collect block
+        %                   boundaries into physical boundaries to simplify
+        %                   getting boundary operators and setting boundary conditions
         function obj = Grid(grids, connections, boundaryGroups)
+            default_arg('boundaryGroups', struct());
             obj.grids = grids;
             obj.connections = connections;
 
@@ -27,7 +30,7 @@
                 obj.nPoints = obj.nPoints + grids{i}.N();
             end
 
-            % if iscell(boundaryGroups)
+            obj.boundaryGroups = boundaryGroups;
         end
 
         function n = size(obj)
@@ -121,13 +124,43 @@
 
         end
 
+        % Find all non interface boundaries of all blocks.
+        % Return their grid.boundaryIdentifiers in a cell array.
         function bs = getBoundaryNames(obj)
-            bs = [];
+            bs = {};
+            for i = 1:obj.nBlocks()
+                candidates = obj.grids{i}.getBoundaryNames();
+                for j = 1:obj.nBlocks()
+                    if ~isempty(obj.connections{i,j})
+                        candidates = setdiff(candidates, obj.connections{i,j}{1});
+                    end
+
+                    if ~isempty(obj.connections{j,i})
+                        candidates = setdiff(candidates, obj.connections{j,i}{2});
+                    end
+                end
+
+                for k = 1:length(candidates)
+                    bs{end+1} = {i, candidates{k}};
+                end
+            end
         end
 
-        % Return coordinates for the given boundary
-        function b = getBoundary(obj, name)
-            b = [];
+        % Return coordinates for the given boundary/boundaryGroup
+        function b = getBoundary(obj, boundary)
+            switch class(boundary)
+                case 'cell'
+                    I = boundary{1};
+                    name = boundary{2};
+                    b = obj.grids{I}.getBoundary(name);
+                case 'multiblock.BoundaryGroup'
+                    b = [];
+                    for i = 1:length(boundary)
+                        b = [b; obj.getBoundary(boundary{i})];
+                    end
+                otherwise
+                    error('Unknown boundary indentifier')
+            end
         end
     end
 end