[R] ?plot: Add an example on how to plot functions to the help of `plot`.

[Paul Menzel]

Am Mittwoch, den 27.07.2011, 18:04 -0400 schrieb David Winsemius:
> On Jul 27, 2011, at 5:53 PM, Paul Menzel wrote:

> > as `plot.function` is not explicitly mentioned in `?plot`.
> 
> Right, but the fact that it _is_ described as a "generic" function  
> will tell the clueful that other methods other than the default method  
> may exist, and that their availability may vary with which packages  
> are loaded.

Of course, when you know what to do it is clear where to look. I just
want to offer a view point from a beginner and adding that little
comment would have saved me half an hour. (Because searching for »r
plotting function« did not result in good hits.)

> > One further comment regarding the examples in `?plot.function`. Trying
> > those in order
> >
> >        op <- par(mfrow = c(2, 2))
> >        chippy <- function(x) sin(cos(x)*exp(-x/2))
> >        plot (chippy, -8, -5)
> >        for(ll in c("", "x", "y", "xy"))
> >        curve(log(1+x), 1, 100, log = ll,
> >              sub = paste("log= '", ll, "'", sep = ""))
> >        par(op)
> >
> > I do not see any effect executing `par(op)` at the end. Reading `? 
> > par` I
> > assume it should go before the for loop?
> 
> No. Read:
> 
> ?par
> 
> It has both a value and a side-effect. Pay particular attention to its  
> value for its first invocation. Then think about why its side-effect  
> is what you want _after_ the loop. Then you may understand what is  
> happening.  Report back to the class. (This isn't in the Introductory  
> material you are reading?)

I messed up and somehow missed to execute `op <- par(mfrow = c(2, 2))`
when first running the examples and jumped to wrong conclusion. I am
sorry for the noise.


Thank you for your patience and help,

Paul
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