# This program calculates the inverse of  (X'X)
# where X is the design matrix produced by 
# Y_{i j} = \mu_i + \epsilon_{i j}, i=1,2,3; j=1,2.
# Created by C. Andy Tsao.  031210

X<-c(1,1,rep(c(0,0),2),0,0,1,1,0,0,0,0,0,0,1,1)
dim(X)<-c(6,3)
X             # The design matrix

A<-t(X)%*%X   # A= X'X
A
solve(A)      # A inverse
A*solve(A)    # AA^(-1) = I

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