#
#  Figure 2.1  Examples of inverse chi-squared densities
#
invchisq <- function(x)(2^(nu/2)*gamma(nu/2))^(-1)*x^(-nu/2-1)*exp(-1/(2*x))
par(lty=1)
nu<-25
curve(invchisq,0,0.5,xlim=c(0,0.5),ylim=c(0,36),n=1000,xlab="x",ylab="p(x)")
segments(0.25,15,0.3,15)
text(0.35,15,"25 d.f.")
par(new=T)
par(lty=2)
nu<-20
curve(invchisq,0,0.5,xlim=c(0,0.5),ylim=c(0,36),xlab="",ylab="")
segments(0.25,17.5,0.3,17.5)
text(0.35,17.5,"20 d.f.")
par(new=T)
par(lty=3)
nu<-15
curve(invchisq,0,0.5,xlim=c(0,0.5),ylim=c(0,36),xlab="",ylab="")
segments(0.25,20,0.3,20)
text(0.35,20,"15 d.f.")
par(new=T)
par(lty=4)
nu<-10
curve(invchisq,0,0.5,xlim=c(0,0.5),ylim=c(0,36),xlab="",ylab="")
segments(0.25,22.5,0.3,22.5)
text(0.35,22.5,"10 d.f.")
par(new=T)
par(lty=5)
nu<-5
curve(invchisq,0,0.5,xlim=c(0,0.5),ylim=c(0,36),xlab="",ylab="")
segments(0.25,25,0.3,25)
text(0.35,25," 5 d.f.")
par(lty="solid")