--- a/operator_def/assemble_op.m	Mon Sep 10 17:48:48 2018 +0200
+++ b/operator_def/assemble_op.m	Mon Sep 10 18:50:29 2018 +0200
@@ -1,14 +1,12 @@
-function [D] = assemble_op(inner_stencil,boundary_block,m)
-  
+function [D] = assemble_op(inner_stencil,boundary_block,m,sign)  
   [height_b, width_b] = size(boundary_block);
   width_i = length(inner_stencil);
   
   max_offset = floor(width_i/2);
   diags = -max_offset:max_offset;
-  
-  
+   
   D = stripeMatrix(inner_stencil, diags, m);
   
   D(1:height_b,1:width_b) = boundary_block;
-  D(m-height_b+1:m,m-width_b+1:m) = rot90( -boundary_block ,2);
+  D(m-height_b+1:m,m-width_b+1:m) = rot90( sign*boundary_block ,2);
 end
\ No newline at end of file