ABSTRACT
I shall describe the method for the simple case -�u = f on n, u l afl = g . ( 1 )
For simplicity I assume that an i s a polygon. The mesh i s supposed in this way: The given domain is covered by a quadrilateral mesh with a natural requirement that all angles a of the quadrilaterals satisfy ° < ao � a � 11" - ao . Each quadrilateral i s divided in two triangles in such a way that neighbours of any internal node create a hexagonal box. In general, the method can be applied for n-gonals with n � 5 . For n = 4 it does not work for quadrilaterals with diagonals which are perpendicular. Let me mention references [1 ] , [2] , [3] where box methods are described giving O(h2 ) error for gradients . In all these references the meshes are built from rectangles or from equilateral triangles or from both these kinds of elements .
