求解三对角矩阵的时候可以用追赶法解方程组的解，文件为追赶法例程，附带Crank-Nicolson格式解对流方程算法(When solving tridiagonal matrix, we can use catch-up method to solve the solution of equations. The file is catch-up method routine, with crank Nicolson scheme to solve the convection equation algorithm)