#
# Written by:
# -- 
# John L. Weatherwax                2009-04-21
# 
# email: wax@alum.mit.edu
# 
# Please send comments and especially bug reports to the
# above email address.
#
# Computations used for the problems in this section of the text.
#
#-----

# Ex 7.45
#
DF = read.csv( "../../Data/CH07/ex7-45.txt", header=TRUE, quote="'" )
n = length(DF$toughness)
s = sd(DF$toughness)
alpha = 0.01
sqrt( (n-1) * s^2 / c( qchisq( 1-alpha/2, n-1 ), qchisq( alpha/2, n-1 ) ) )


# Ex 7.46
#
DF = read.csv( "../../Data/CH07/ex7-46.txt", header=TRUE, quote="'" )
X = DF$pressure..kN.m2.

qqnorm(X)
qqline(X)
grid()

n = length(X)
s = sd(X)
alpha = 0.05
sqrt( (n-1) * s^2 / qchisq( alpha, n-1 ) )