# This code is stored in:      chiden.ssc

#================================================#
# chisq.density.plot()                           #
# ------------------------                       #
# Input : degrees of freedom; it can be a vector.#
#           (e.g.) chisq.density.plot(c(1,2,5,7))#
#           creates curves for  df = 1,3,5,and 7 #
# Output: density plot of chisquare distribution.#
#                                                #
##################################################

chisq.density.plot <- function(df)
{	
   x <- seq(.001,10,,50)

   # draw x,y axis and title
	
   plot(c(0,10), c(0,.5), type="n", 
      xlab="x", ylab="f(x;df)",
      main="Central Chi-Square Densities")

   for(i in 1:length(df)) {
      lty.num <- 3*i-2          # specify the line types.
      f.x <- dchisq(x,df[i])    # calculate density.
      lines(x, f.x, type="l",lty=lty.num)   # draw spline.
    }

   # The following lines are for legends;
	
       legend( x = rep(5,length(df)) , 
	  y = rep(.45,length(df)) ,
	  legend = paste(as.character(df),"df") , 
	  lty = seq(1,by=3,length=length(df)) ,
	  bty = "n")
}



#  This function can be executed with
#  the following commands.  The source( )
#  function enters the entire file into
#  the command window and executes all
#  of the commands in the file.
#
#  source("chiden.ssc")
#  par(fin=c(6,8),cex=1.2,mex=1.5,lwd=4)
#  chisq.density.plot(c(1,3,5,7))