n<-100
set.seed(101)
x<-runif(n,0,100)

y<-2.0+1.5*x

plot(x,y)

y<-2.0+1.5*x+rnorm(n)
plot(x,y)

y<-2.0+1.5*x+rnorm(n)*20
plot(x,y,pch=19)

y<-2.0+1.5*x+rnorm(n)*20
points(x,y,pch=19,col='red')

y<-2.0+1.5*x+rnorm(n)*20
points(x,y,pch=3,col='green')

set.seed(476)
y1<-2.0+1.5*x+rnorm(n)*20
y2<-2.0+1.5*x+rnorm(n)*20
y3<-2.0+1.5*x+rnorm(n)*20

####################################

par(mfrow=c(2,2),mar=c(2,2,2,2))
plot(x,y1,pch=19)
fit1<-lm(y1~x)
abline(coef(fit1),col='red')
abline(2,1.5,col='blue')

plot(x,y2,pch=19)
fit2<-lm(y2~x)
abline(coef(fit2),col='red')
abline(2,1.5,col='blue')

plot(x,y3,pch=19)
fit3<-lm(y3~x)
abline(coef(fit3),col='red')
abline(2,1.5,col='blue')

####################################

summary(fit1)

pdf('myplot.pdf')
plot(x,y1,pch=19)
fit1<-lm(y1~x)
abline(coef(fit1),col='red')
dev.off()