--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+sbp/+implementations/d2_variable_hollow_2.m	Thu Mar 10 16:54:26 2022 +0100
@@ -0,0 +1,56 @@
+function [H, HI, D1, D2, e_l, e_r, d1_l, d1_r] = d2_variable_hollow_2(m,h)
+
+    BP = 1;
+    if(m<2*BP)
+        error(['Operator requires at least ' num2str(2*BP) ' grid points']);
+    end
+
+    % Norm
+    Hv = ones(m,1);
+    Hv(1) = 1/2;
+    Hv(m:m) = 1/2;
+    Hv = h*Hv;
+    H = spdiag(Hv, 0);
+    HI = spdiag(1./Hv, 0);
+
+
+    % Boundary operators
+    e_l = sparse(m,1);
+    e_l(1) = 1;
+    e_r = rot90(e_l, 2);
+
+    d1_l = sparse(m,1);
+    d1_l(1:3) = 1/h*[-3/2 2 -1/2];
+    d1_r = -rot90(d1_l, 2);
+
+    % D1 operator
+    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');
+
+
+    nBP = 2;
+    M = sparse(m,m);
+    coeffs = load('sbplib/+sbp/+implementations/coeffs_d2_variable_2.mat');
+
+    function D2 = D2_fun(c)
+        M_l = zeros(nBP, coeffs.nBPC);
+        M_r = zeros(nBP, coeffs.nBPC);
+
+        for i=1:coeffs.nBPC
+            M_l = M_l + coeffs.C_l{i}*c(i);
+            M_r = M_r + coeffs.C_r{i}*c(m-coeffs.nBPC+i);
+        end
+
+        M(1:nBP, 1:coeffs.nBPC) = M_l;
+        M(m-nBP+1:m, m-coeffs.nBPC+1:m) = M_r;
+
+        D2 = M/h^2;
+    end
+    D2 = @D2_fun;
+end
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