--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+sbp/D4Variable.m	Tue Feb 07 16:09:02 2017 +0100
@@ -0,0 +1,75 @@
+classdef D4Variable < sbp.OpSet
+    properties
+        m    % Number of grid points.
+        h    % Step size
+        x    % grid
+        H    % Norm matrix
+        HI   % H^-1
+        D1   % SBP operator approximating first derivative
+        D2   % SBP operator for second derivative
+        D4   % SBP operator for fourth derivative
+        Q    % Skew-symmetric matrix
+        M    % Norm matrix, second derivative
+        M4   % Norm matrix, fourth derivative
+        e_l,  e_r  % Left and right boundary operator
+        d1_l, d1_r % Left and right boundary first derivative
+        d2_l, d2_r % Left and right boundary second derivative
+        d3_l, d3_r % Left and right boundary third derivative
+        borrowing % Struct with borrowing limits for different norm matrices
+        order
+    end
+
+    methods
+        function obj = D4Variable(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)';
+
+            if order == 2
+                [H, HI, D1, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                    sbp.implementations.d4_variable_2(m, obj.h);
+                obj.borrowing.M.d1 = 0.4000;
+                obj.borrowing.N.S2 = 1.2500;
+                obj.borrowing.N.S3 = 0.4000;
+            elseif order == 4
+                [H, HI, D1, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                    sbp.implementations.d4_variable_4(m, obj.h);
+                obj.borrowing.M.d1 = 0.2508;
+                obj.borrowing.N.S2 = 0.5055;
+                obj.borrowing.N.S3 = 0.9290;
+            elseif order == 6
+                [H, HI, D1, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                    sbp.implementations.d4_variable_6(m, obj.h);
+                obj.borrowing.M.d1 = 0.1878;
+                obj.borrowing.N.S2 = 0.3259;
+                obj.borrowing.N.S3 = 0.1580;
+            else
+                error('Invalid operator order.');
+            end
+
+            obj.m = m;
+            obj.order = order;
+
+            obj.H    = H;
+            obj.HI   = HI;
+            obj.D1   = D1;
+            obj.D2   = D2;
+            obj.D4   = D4;
+            obj.M4   = M4;
+            obj.e_l  = e_l;
+            obj.e_r  = e_r;
+            obj.d1_l = d1_l;
+            obj.d1_r = d1_r;
+            obj.d2_l = d2_l;
+            obj.d2_r = d2_r;
+            obj.d3_l = d3_l;
+            obj.d3_r = d3_r;
+        end
+
+        function str = string(obj)
+            str = [class(obj) '_' num2str(obj.order)];
+        end
+    end
+end
\ No newline at end of file