说明：  计算二维斜激波各个变量之间的关系，输入波前马赫数，sita,beta之中的任何两个，可以求出压力，密度，马赫数等波后量与波前量的比值
(Relationship between the variables of the calculation of two-dimensional oblique shock, out of any two of the Mach number, sita, beta, the input wavefront, which can be determined pressure, the ratio of the amount of density, Mach wave after the amount of wavefront)