\begin{Schunk}
\begin{Sinput}
 xvals <- seq(0,30,length.out=1000)
 chisquare1 <- dchisq(xvals, df=5)
 chisquare2 <- dchisq(xvals, df=10)
 chisquare3 <- dchisq(xvals, df=20)
 plot(xvals, chisquare1, type="l", xlab=expression(chi^2), ylab="probability density",  ylim=c(0,0.4), main="")
 lines(xvals, chisquare2, lty=2)
 lines(xvals, chisquare3, lty=3)
 legend("topright",legend=(c(expression(nu==5), expression(nu==10),expression(nu==20))),lty=1:3)
\end{Sinput}
\end{Schunk}
