--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+sbp/D4Variable.m	Fri Sep 23 10:52:53 2016 +0200
@@ -0,0 +1,120 @@
+classdef D4CompatibleVariable < 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
+        D3   % SBP operator for third derivative
+        Q3   % Skew-symmetric matrix in third derivative
+        d2_l % Left boundary second derivative
+        d2_r % Right boundary second derivative
+        D4   % SBP operator for fourth derivative
+        M4   % Norm matrix, fourth derivative
+        d3_l % Left boundary third derivative
+        d3_r % Right boundary third derivative
+        m    % Number of grid points.
+        h    % Step size
+        x    % grid
+        borrowing % Struct with borrowing limits for different norm matrices
+    end
+
+    methods
+        function obj = D4CompatibleVariable(m, lim, order, opt)
+            default_arg('opt', '')
+
+            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
+                [obj.H, obj.HI, ~, obj.D2, ~, obj.D4, obj.e_l, obj.e_r,...
+                 obj.M4, ~, obj.d2_l, obj.d2_r, obj.d3_l,...
+                    obj.d3_r, obj.d1_l, obj.d1_r] =...
+                    sbp.implementations.d4_compatible_halfvariable_2(m,obj.h);
+                obj.borrowing.N.S2 = 1.2500;
+                obj.borrowing.N.S3 = 0.4000;
+
+            elseif order == 4
+                switch opt
+                    case 'min_boundary_points'
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.higher_variable4_min_boundary_points(m, obj.h);
+                        % obj.borrowing.N.S2 = 0.5055;
+                        % obj.borrowing.N.S3 = 0.9290;
+                    otherwise
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.implementations.d4_compatible_halfvariable_4(m, obj.h);
+                        obj.borrowing.N.S2 = 0.5055;
+                        obj.borrowing.N.S3 = 0.9290;
+                end
+
+            elseif order == 6
+                switch opt
+                    case '2'
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.higher_variable6_2(m, obj.h);
+                        % obj.borrowing.N.S2 = 0.3259;
+                        % obj.borrowing.N.S3 = 0.1580;
+                    case '3'
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.higher_variable6_3(m, obj.h);
+                        % obj.borrowing.N.S2 = 0.3259;
+                        % obj.borrowing.N.S3 = 0.1580;
+                    case 'min_boundary_points'
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.higher_variable6_min_boundary_points(m, obj.h);
+                        % obj.borrowing.N.S2 = 0.3259;
+                        % obj.borrowing.N.S3 = 0.1580;
+                    otherwise
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.implementations.d4_compatible_halfvariable_6(m, obj.h);
+                        obj.borrowing.N.S2 = 0.3259;
+                        obj.borrowing.N.S3 = 0.1580;
+                end
+
+            elseif order == 8
+                switch opt
+                    case 'min_boundary_points'
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.higher_variable8_min_boundary_points(m, obj.h);
+                        % obj.borrowing.N.S2 = 0.3259;
+                        % obj.borrowing.N.S3 = 0.1580;
+                    otherwise
+                        [H, HI, D2, D4, e_l, e_r, M4, d2_l, d2_r, d3_l, d3_r, d1_l, d1_r] = ...
+                            sbp.higher_variable8_higher_boundary_order(m, obj.h);
+                        % obj.borrowing.N.S2 = 0.3259;
+                        % obj.borrowing.N.S3 = 0.1580;
+                    end
+            else
+                error('Invalid operator order.');
+            end
+
+            obj.m = m;
+
+            obj.H    = H;
+            obj.HI   = HI;
+            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;
+
+            obj.D1 = [];
+            obj.D3 = [];
+        end
+    end
+end
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