> m=0:200;x1=c(sample(m,80));x2=c(sample(m,80));x3=c(sample(m,80));x4=c(sample(m,80))
> u=rnorm(80,0,9);Y=numeric(80);Y=20.11+20*x1+11*x2+44*x3+30*x4+u
> n=cbind(Y,x1,x2,x3)
> b1=numeric(300); b2=numeric(300); b3=numeric(300)
> x1=numeric(30); x2=numeric(30); x3=numeric(30);y=numeric(30)
> for(i in 1:300){
+ x1=sample(n[,2],30); x2=sample(n[,3],30);x3=sample(n[,4],30)
+ ranky1=match(x1,n) ; y=n[ranky1,2];ranky2=match(x2,n) ; y=n[ranky2,3];
+ ranky3=match(x3,n) ; y=n[ranky3,4];
+ lm=lm(y~x1+x2+x3)
+ b1= lm$coefficients[[1]];b2=lm$coefficients[[2]];b3=lm$coefficients[[3]];b4=lm$coefficients[[4]]}
错误: 下标出界
> mean(b1)
[1] 0
对多元回归方程进行最小二乘法确定系数时,总是得到上述提示,这是为什么,错在哪里,应怎样改正???



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