[R] how to use plot.lda included in MASS package?

[wu sz]

Hi there,

I am a master student in Denmark, and apply R to analyze the drug data.

I use the function 'lda' to obtain a linear discriminant object, and
then wish to use 'plot.lda' to do the plot on this object like below.

drug.lda <- lda(Inhibition ~ NET_CHARGE + PKA_1 + MW + MLOGP, 
                      data = drug.class, method = "moment")

plot.lda(drug.lda, panel = panel.lda, cex = 0.7, dimen = 1, abbrev = FALSE, 
            type ="density")

but I got an error message: Error: couldn't find function "plot.lda"
and then I tried 

plot(drug.lda, panel = panel.lda, cex = 0.7, dimen = 1, abbrev = FALSE, 
            type ="density")

still an error message was returned: Error in plot.default(drug.lda,
panel = panel.lda, cex = 0.7,  : argument 2 matches multiple formal
arguments

Also I can't find this panel function, panel.lda anywhere. Do you know
how to use this plot function?

Thanks a lot!
wsz