--- a/+sbp/InterpOpsOP.m	Tue Dec 04 12:54:33 2018 +0100
+++ b/+sbp/InterpOpsOP.m	Tue Dec 04 14:06:42 2018 -0800
@@ -7,9 +7,9 @@
     end
 
     methods
-        % x_u, x_v         --   vectors of the coordinate that varies along the boundary
+        % m_u, m_v         --   number of grid points along the interface
         % order_u, order_v --   order of accuracy in the different blocks
-        function obj = InterpOpsOP(x_u, x_v, order_u, order_v)
+        function obj = InterpOpsOP(m_u, m_v, order_u, order_v)
 
             assert(order_u == order_v,...
                     'InterpOpsOP: Different orders of accuracy not available');
@@ -27,25 +27,22 @@
                 error('InterpOpsOP: Order of accuracy %d not available.', order_u);
             end
 
-            m_u = length(x_u) - 1;
-            m_v = length(x_v) - 1;
-
             Iu2v = struct;
             Iv2u = struct;
 
-            if m_u/m_v == 2
+            if (m_u-1)/(m_v-1) == 2
                 % Block u is fine, v is coarse
                 m_C = m_v;
-                [Iv2u.good, Iu2v.bad] = intOpSet(m_C+1, 1, 'C2F');
-                [Iv2u.bad, Iu2v.good] = intOpSet(m_C+1, 1, 'F2C');
+                [Iv2u.good, Iu2v.bad] = intOpSet(m_C, 1, 'C2F');
+                [Iv2u.bad, Iu2v.good] = intOpSet(m_C, 1, 'F2C');
 
-            elseif m_v/m_u == 2
+            elseif (m_v-1)/(m_u-1) == 2
                 % Block v is fine, u is coarse
                 m_C = m_u;
-                [Iu2v.good, Iv2u.bad] = intOpSet(m_C+1, 1, 'C2F');
-                [Iu2v.bad, Iv2u.good] = intOpSet(m_C+1, 1, 'F2C');
+                [Iu2v.good, Iv2u.bad] = intOpSet(m_C, 1, 'C2F');
+                [Iu2v.bad, Iv2u.good] = intOpSet(m_C, 1, 'F2C');
             else
-                error('InterpOpsOP: Interpolation operators for grid ratio %f have not yet been constructed', m_u/m_v);
+                error('InterpOpsOP: Interpolation operators for grid ratio %f have not yet been constructed', (m_u-1)/(m_v-1));
             end
 
             obj.Iu2v = Iu2v;