############################################################################
#         R ROUTINE FOR PLOTTING ONE-DIMENSIONAL FUNCTIONS
#
#         (by Jeffrey S. Rosenthal, probability.ca, 2007)
# 
# The statistical software R includes various plotting routines like
# "plot" and "curve", which usually work well but sometimes fail
# [e.g. for the constant function "f = function(x) return(5)"].
# So, I provide here a simpler function-plotting routine, which only
# works for one-dimensional functions, and which runs slowly, but
# which does always(?) work as expected.  (Released under GPL.)
############################################################################

plotfunction = function(ff, from=xlim[1], to=xlim[2], col="black",
	add=FALSE, xlim=c(0,1), numpoints=1000 ) {
    xlist = ylist = NULL;
    ymin = +Inf;
    ymax = -Inf;
    for (i in 1:numpoints) {
        xval = from + (to-from) * i / numpoints;
        yval = ff(xval);
        xlist = c(xlist, xval);
        ylist = c(ylist, yval);
	if (yval < ymin)
	    ymin = yval;
	if (yval > ymax)
	    ymax = yval;
    }
    if (add==FALSE) {
	plot( c((from+to)/2, (ymin+ymax)/2), type='n',
		xlim=c(from,to), ylim=c(ymin,ymax), xlab="x",
		ylab=paste( deparse(substitute(ff)), "(x)", sep="" )
	);
    }
    lines(xlist, ylist, col=col);
}