--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+sbp/+implementations/d1_upwind_4.m	Fri Sep 23 10:40:12 2016 +0200
@@ -0,0 +1,36 @@
+function [H, HI, Dp, Dm, e_1, e_m] = d1_upwind_4(m,h)
+
+    if(m<8)
+        error('Operator requires at least 8 grid points');
+    end
+
+    Hv=ones(m,1);
+    Hv(1:4)=[49/144 61/48 41/48 149/144];
+    Hv(m-3:m)=rot90(Hv(1:4),2);
+    Hv = Hv*h;
+    H = spdiag(Hv,0);
+    HI = spdiag(1./Hv,0);
+
+    q_diags   = [-1, 0, 1, 2 3];
+    q_stencil = [-1/4 -5/6 3/2 -1/2 1/12];
+    Qp = stripeMatrix(q_stencil, q_diags,m);
+
+    Q_U = [
+        -0.1e1/0.48e2    0.205e3/0.288e3 -0.29e2/0.144e3 0.1e1/0.96e2;
+        -0.169e3/0.288e3 -0.11e2/0.48e2  0.33e2/0.32e2   -0.43e2/0.144e3;
+        0.11e2/0.144e3   -0.13e2/0.32e2  -0.29e2/0.48e2  0.389e3/0.288e3;
+        0.1e1/0.32e2     -0.11e2/0.144e3 -0.65e2/0.288e3 -0.13e2/0.16e2;
+    ];
+
+    Qp(1:4,1:4)=Q_U;
+    Qp(m-3:m,m-3:m)=rot90(Q_U,2)'; %%% This is different from standard SBP
+
+    Qm=-Qp';
+
+    e_1=sparse(m,1);e_1(1)=1;
+    e_m=sparse(m,1);e_m(m)=1;
+
+    Dp=HI*(Qp-1/2*(e_1*e_1')+1/2*(e_m*e_m')) ;
+
+    Dm=HI*(Qm-1/2*(e_1*e_1')+1/2*(e_m*e_m')) ;
+end