[R] how to use biplot to show PC1 and PC3 or else?

[xin]

hello:
I am trying to use biplot show relationship between PC1 and PC3 of princomp.
There is example showing how to do it with PC1 and PC2. But I am totally out
of idea for PC1 and PC3. Thanks very much for your kind help.

Best Wishes,

yours,
xin