--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+sbp/D2Variable.m	Fri Sep 23 10:40:12 2016 +0200
@@ -0,0 +1,49 @@
+classdef D2Variable < sbp.OpSet
+    properties
+        D1 % SBP operator approximating first derivative
+        H % Norm matrix
+        HI % H^-1
+        Q % Skew-symmetric matrix
+        e_l % Left boundary operator
+        e_r % Right boundary operator
+        D2 % SBP operator for second derivative
+        M % Norm matrix, second derivative
+        d1_l % Left boundary first derivative
+        d1_r % Right boundary first derivative
+        m % Number of grid points.
+        h % Step size
+        x % grid
+        borrowing % Struct with borrowing limits for different norm matrices
+    end
+
+    methods
+        function obj = D2Variable(m,lim,order)
+            
+            x_l = lim{1};
+            x_r = lim{2};
+            L = x_r-x_l;
+            obj.h = L/(m-1);
+            obj.x = linspace(x_l,x_r,m)';
+
+            switch order
+                case 4
+                    [obj.H, obj.HI, obj.D1, obj.D2, obj.e_l,...
+                        obj.e_r, obj.d1_l, obj.d1_r] = ...
+                        sbp.implementations.d2_variable_4(m,obj.h);
+                    obj.borrowing.M.S = 0.2505765857;
+                otherwise
+                    error('Invalid operator order %d.',order);
+            end
+
+            obj.m = m;
+            obj.M = [];
+
+        end
+    end
+
+end
+
+
+
+
+