# overlay.R
# written by Bret Larget
# January 23, 2008

# This function is meant to be used as the panel argument
# with histogram from the lattice package.
#
# For example, if you have a variable y and you want to overlay a normal curve
# over the histogram of y, you would use this call.
#
# > plot( histogram(~ y,type="density",panel=overlayNormal ) )

overlayNormal = function(x,ncol="black",nlwd=2,...) {
  panel.histogram(x,...)
  panel.mathdensity(dmath = dnorm, col=ncol, args = list(mean=mean(x),sd=sd(x)),lwd=nlwd)
}