matlab ar模型怎么计算出系数,y=a1*x1+a2*x2+a3*x3+a4*x4+et,怎么求a1,a2,a3,a4,求详细程序,

matlab ar模型怎么计算出系数,y=a1*x1+a2*x2+a3*x3+a4*x4+et,怎么求a1,a2,a3,a4,求详细程序,

x=[x1 x2 x3 x4]; % 定义样本空间
y %测量值
a=[a1 a2 a3 a4]; %待求系数
%Matrix form of equation
y=x*a;
a=x\y;