--- a/+sbp/+implementations/d2_2.m	Fri Sep 09 11:03:13 2016 +0200
+++ b/+sbp/+implementations/d2_2.m	Fri Sep 09 14:53:41 2016 +0200
@@ -5,29 +5,35 @@
         error(['Operator requires at least ' num2str(2*BP) ' grid points']);
     end
 
-    e_1=zeros(m,1);e_1(1)=1;
-    e_m=zeros(m,1);e_m(m)=1;
+    e_1=sparse(m,1);e_1(1)=1;
+    e_m=sparse(m,1);e_m(m)=1;
 
-    H=(eye(m,m));H(1,1)=0.5;H(m,m)=0.5;
+    H=(speye(m,m));H(1,1)=0.5;H(m,m)=0.5;
     H=h*H;
     HI=inv(H);
-
-    D1=((.5*diag(ones(m-1,1),1)-.5*diag(ones(m-1,1),-1)));
+    
+    diags   = -1:1;
+    stencil = [-1/2 0 1/2];
+    D1 = stripeMatrix(stencil, diags, m);
+    
     D1(1,1)=-1;D1(1,2)=1;D1(m,m-1)=-1;D1(m,m)=1;
     D1(m,m-1)=-1;D1(m,m)=1;
     D1=D1/h;
 
-    Q=H*D1 + 1/2*e_1*e_1' - 1/2*e_m*e_m';
+    Q=H*D1 + 1/2*(e_1*e_1') - 1/2*(e_m*e_m');
 
-    D2=((diag(ones(m-1,1),1)+diag(ones(m-1,1),-1)-2*diag(ones(m,1),0)));
+    diags   = -1:1;
+    stencil = [1 -2 1];
+    D2 = stripeMatrix(stencil, diags, m);
+    
     D2(1,1)=1;D2(1,2)=-2;D2(1,3)=1;
     D2(m,m-2)=1;D2(m,m-1)=-2;D2(m,m)=1;
     D2=D2/h^2;
 
     S_U=[-3/2, 2, -1/2]/h;
-    S_1=zeros(1,m);
+    S_1=sparse(1,m);
     S_1(1:3)=S_U;
-    S_m=zeros(1,m);
+    S_m=sparse(1,m);
     S_m(m-2:m)=fliplr(-S_U);