[R] pairs function from graphics

[Jungyeon Yoon]

Hi,

I have two questions about options for panel, upper.panel, lower.panel in 
pairs().
1. I see examples using panel.smooth, panel.corr, panel.hist.
Are there any plots that can be used here?

2. Can we have different plots in upper diagonal? For example, in a matrix 
of scatterplots, I want to know if we can have a scatter plot for an 
element (1,2) and then one smooth plot for an element (1,3).

Thanks.