n=100 #设置循环100次
p=array(n);q=array(n)　＃此2向量分别放系数b1,b2
for (i in 1:n) {
x=runif(300)
e=rnorm(300,0,4)
y=1+3*x+e
r=lm(y~x)
p[i]=r$coefficients[1] #说明：因估计标准误不知如何表示，故在此未列出，只求了b1,b2的均值
q[i]=r$coefficients[2]
}
b1=mean(p)
b2=mean(q)
b1
b2

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x <- runif(300);
y <- 1 + 3*x + 2*rnorm(300,0,1);
summary(fitted <- lm(y~x));
fitted$coef;
var(fitted$res);

N <- 100;
est <- matrix(numeric(N*3), ncol = 3)
for (i in 1:N){
        x <- runif(300);
        y <- 1 + 3*x + 2*rnorm(300,0,1);
        fitted <- lm(y~x);
        est[i,] <- c(fitted$coef, var(fitted$res));
}
colMeans(est)

n=100 #设置循环100次
p=array(n);q=array(n)　＃此2向量分别放系数b1,b2
for (i in 1:n) {
x=runif(300)
e=rnorm(300,0,4)
y=1+3*x+e
r=lm(y~x)
p[i]=r$coefficients[1] #说明：因估计标准误不知如何表示，故在此未列出，只求了b1,b2的均值
q[i]=r$coefficients[2]
}
b1=mean(p)
b2=mean(q)
b1
b2