--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+sbp/+implementations/d1_noneq_4.m	Mon Sep 12 12:53:02 2016 +0200
@@ -0,0 +1,114 @@
+function [D1,H,x,h] = d1_noneq_4(N,L)
+
+% L: Domain length
+% N: Number of grid points
+if(nargin < 2)
+    L = 1;
+end
+
+if(N<8)
+    error('Operator requires at least 8 grid points');
+end
+
+% BP: Number of boundary points
+% m:  Number of nonequidistant spacings
+% order: Accuracy of interior stencil
+BP = 4;
+m = 2;
+order = 4;
+
+%%%% Non-equidistant grid points %%%%%
+x0 =  0.0000000000000e+00;
+x1 =  6.8764546205559e-01;
+x2 =  1.8022115125776e+00;
+x3 =  2.8022115125776e+00;
+x4 =  3.8022115125776e+00;
+
+xb = sparse(m+1,1);
+for i = 0:m
+    xb(i+1) = eval(['x' num2str(i)]);
+end
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%% Compute h %%%%%%%%%%
+h = L/(2*xb(end) + N-1-2*m);
+%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%% Define grid %%%%%%%%
+x = h*[xb; linspace(xb(end)+1,L/h-xb(end)-1,N-2*(m+1))'; L/h-flip(xb) ];
+%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%% Norm matrix %%%%%%%%
+P = sparse(BP,1);
+%#ok<*NASGU>
+P0 =  2.1259737557798e-01;
+P1 =  1.0260290400758e+00;
+P2 =  1.0775123588954e+00;
+P3 =  9.8607273802835e-01;
+
+for i = 0:BP-1
+    P(i+1) = eval(['P' num2str(i)]);
+end
+
+H = ones(N,1);
+H(1:BP) = P;
+H(end-BP+1:end) = flip(P);
+H = spdiags(h*H,0,N,N);
+%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%% Q matrix %%%%%%%%%%%
+
+% interior stencil
+switch order
+    case 2
+        d = [-1/2,0,1/2];
+    case 4
+        d = [1/12,-2/3,0,2/3,-1/12];
+    case 6
+        d = [-1/60,3/20,-3/4,0,3/4,-3/20,1/60];
+    case 8
+        d = [1/280,-4/105,1/5,-4/5,0,4/5,-1/5,4/105,-1/280];
+    case 10
+        d = [-1/1260,5/504,-5/84,5/21,-5/6,0,5/6,-5/21,5/84,-5/504,1/1260];
+    case 12
+        d = [1/5544,-1/385,1/56,-5/63,15/56,-6/7,0,6/7,-15/56,5/63,-1/56,1/385,-1/5544];
+end
+d = repmat(d,N,1);
+Q = spdiags(d,-order/2:order/2,N,N);
+
+% Boundaries
+Q0_0 = -5.0000000000000e-01;
+Q0_1 =  6.5605279837843e-01;
+Q0_2 = -1.9875859409017e-01;
+Q0_3 =  4.2705795711740e-02;
+Q0_4 =  0.0000000000000e+00;
+Q0_5 =  0.0000000000000e+00;
+Q1_0 = -6.5605279837843e-01;
+Q1_1 =  0.0000000000000e+00;
+Q1_2 =  8.1236966439895e-01;
+Q1_3 = -1.5631686602052e-01;
+Q1_4 =  0.0000000000000e+00;
+Q1_5 =  0.0000000000000e+00;
+Q2_0 =  1.9875859409017e-01;
+Q2_1 = -8.1236966439895e-01;
+Q2_2 =  0.0000000000000e+00;
+Q2_3 =  6.9694440364211e-01;
+Q2_4 = -8.3333333333333e-02;
+Q2_5 =  0.0000000000000e+00;
+Q3_0 = -4.2705795711740e-02;
+Q3_1 =  1.5631686602052e-01;
+Q3_2 = -6.9694440364211e-01;
+Q3_3 =  0.0000000000000e+00;
+Q3_4 =  6.6666666666667e-01;
+Q3_5 = -8.3333333333333e-02;
+for i = 1:BP
+    for j = 1:BP
+        Q(i,j) = eval(['Q' num2str(i-1) '_' num2str(j-1)]);
+        Q(N+1-i,N+1-j) = -eval(['Q' num2str(i-1) '_' num2str(j-1)]);
+    end
+end
+%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%% Difference operator %%
+D1 = H\Q;
+%%%%%%%%%%%%%%%%%%%%%%%%%%%
\ No newline at end of file