--- a/+sbp/+implementations/d2_noneq_variable_6.m	Fri Oct 14 14:42:32 2022 +0200
+++ b/+sbp/+implementations/d2_noneq_variable_6.m	Sat Oct 15 15:48:20 2022 +0200
@@ -138,6 +138,8 @@
 
     % Helper functions for constructing D2(c)
     % TODO: Consider changing sparse(diag(...)) to spdiags(....)
+    min_inds = sbp.implementations.d2_sparsity_pattern_inds(m, order, BP, 0, 3);
+    nonmin_inds = sbp.implementations.d2_sparsity_pattern_inds(m, order, BP, 1, 3);
 
     % Minimal 7 point stencil width
     function D2 = D2_fun_minimal(c)
@@ -152,6 +154,11 @@
         % Remainder term added to wide second derivative operator
         R = (1/3600 / h) * transpose(DD_6) * C1 * DD_6 + (1/600 / h) * transpose(DD_5) * C2 * DD_5 + (1/80 / h) * transpose(DD_4) * C3 * DD_4;
         D2 = D1 * C1 * D1 - H \ R;
+
+        % Remove potential round off zeros
+        D2_tmp = sparse(m,m);
+        D2_tmp(min_inds) = D2(min_inds);
+        D2 = D2_tmp;
     end
 
     %  Non-minimal 9 point stencil width
@@ -165,6 +172,11 @@
         % Remainder term added to wide second derivative operator
         R = (1/3600 / h) * transpose(DD_6) * C1 * DD_6 + (1/600 / h) * transpose(DD_5) * C2 * DD_5;
         D2 = D1 * C1 * D1 - H \ R;
+
+        % Remove potential round off zeros
+        D2_tmp = sparse(m,m);
+        D2_tmp(nonmin_inds) = D2(nonmin_inds);
+        D2 = D2_tmp;
     end
 
     % Wide stencil