“…The first one is the fitted operator method, which reflects the qualitative behavior of the solution; such fitted methods can be found in [3 − 5, 22, 26, 28] and references therein. The second one is the fitted mesh method, which contains finite difference operators on specially designed mesh in the boundary-layer regions, such as Shishkin mesh [5,22,27] and grid equidistribution [18,23,25].…”