根据已知的三维离散数据（x,y,z）,在MATLAB中利用此函数进行三维曲面拟合，再根据polyval2d得出拟合函数的系数矩阵。,according to 3D discrete datum (x,y,z),use this function in MATLAB to fit 3D surface, and use polyval2d to get coefficient matrix