说明：  一维稳态对流扩散方程，边界x=0,x=L,采用中心差分，一阶迎风，混合格式和Quick格式对P=1，5,10作图
(One-dimensional steady-state convection-diffusion equation, boundary x = 0 and x = L, the center differential, a first-order upwind, mixed formats and Quick Format P = 1,5,10 mapping)