[R] How to plot two graphs on one single plot?

[Yun Zhang]

Hi,

I am trying to plot two distribution graph on one plot. But I dont know 
how. I set them to the same x, y limit, even same x, y labels.

Code:
 x1=rnorm(25, mean=0, sd=1)
 y1=dnorm(x1, mean=0, sd=1)

 x2=rnorm(25, mean=0, sd=1)
 y2=dnorm(x2, mean=0, sd=1)
 plot(x1, y1, type='p', xlim=range(x1,x2), ylim=range(y1, y2), xlab='x', 
ylab='y')
 plot(x2, y2, type='p', col="red", xlab='x', ylab='y')

They just dont show up in one plot.

Any hint will be very helpful.

Thanks,
Yun