ABSTRACT
This chapter introduces some basic notions and results related to the theory of Pragmatic General Multicasts (FEMs) in the two-dimensional case. There are many ways to transform the geometry of the given region. In choosing the form of a transformation, one must keep in mind its ultimate use—namely, the grid approximations and resulting grid systems that will be obtained. The chapter focuses on the possible use of an additive removal of singularities suggested by Kantorovich for numerical integration and introduced in equations for improving the accuracy of FEMs. The extremely important questions of obtaining a posteriori estimates and adaptive procedures for improving the accuracy of the grid methods have been the center of attention of many investigators. The role of hierarchical basis in working with polynomials of higher degree is very significant and sometimes heuristic approaches of recursive subdivision of the grid are applied.
