[R] About "cex=": how to improve resolution?

[Luca Quaglia]

Hi,

I need to plot a graph with a circle of radius 1 and
with a series of points of different size. The size of
these points compared to the fixed circle is important
and bears a meaning.

Here is the a simplified version of the code I'm
using:

x<-seq(0,2,by=0.2)
y<-x
z<-seq(0,1,by=0.1)
angle<-pi/180*c(0:359)
par(pty="s")
plot(-2:2,-2:2,type="n")
lines(cos(angle),sin(angle))
points(x,y,cex=z)

I obtain points of the same size when
cex=0.1/0.2/0.3/0.4 or cex=0.5/0.6/0.7 or
cex=0.8/0.9/1.0.

Please, does anyone know if there is a way of
improving the resolution of cex in order to have 10
points *all* of different size (respecting the above
written different values of cex)? The circle is fixed
of radius 1 and the values of cex are in relation with
that and they shouldn't be modified.

Thanks, Luca