Plot two graphs in same plot in R

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I would like to plot y1 and
y2 in the same plot.

x <-
            seq(-2, 2, 0.05)
y1 <- pnorm(x)
y2 <- pnorm(x, 1,
            1)
plot(x, y1, type = "l", col = "red")
plot(x, y2, type = "l", col
            =
            "green")

But
when I do it like this, they are not plotted in the same plot
together.

In Matlab one can do hold
on, but does anyone know how to do this in R?

Answer

lines() or
points() will add to the existing graph, but will not create a
new window. So you'd need to
do

plot(x,y1,type="l",col="red")
lines(x,y2,col="green")