假定已經有許多應用采用了程序1 - 1 5中所定義的C u r r e n c y類，現在我們想要對C u r r e n c y類
的描述進行修改，使其應用頻率最高的兩個函數A d d和I n c r e m e n t可以運行得更快，從而提高應
用程序的執行速度。由于用戶僅能通過p u b l i c部分所提供的接口與C u r r e n c y類進行交互，
％ A 2D homogeneous convection-diffusion case (u=exp(-ex*deta*x-ex*deta*y) with a square with
％ all Dirichlet boundary, note that reaction coefficient is not zero
％ by indirect BKM
A 2D homogeneous Helmholtz case (u=sin(x)cos(y) with a square) with
％ two Dirichlet edges (x=1,y=1) and two Neumann edges (x=0,y=0)
％ by indirect symmetric BKM
