dados<-read.table("d:\\Dados\\combustível.txt", header=TRUE)

attach(dados)

X<-cbind(1, X1, X2, X3, X4)

t(X) %*% X

beta.chapeu = solve( t(X) %*% X) %*% t(X) %*% Y

 lm(Y~-1+X)

 anova( lm(Y~-1+X))

 SQRnc = t(beta.chapeu ) %*% t(X) %*% Y

 SQRc = SQRnc - n * mean(Y)^2
 
 H = X %*% solve(t(X) %*% X) %*% t(X)

 I = diag(rep(1,n))

 SQRes = t(Y) %*% (I-H) %*% Y

 fit.model<-lm(Y~-1+X)

 anova( lm(Y~-1+X))

 library(alr3)

 # pure.error.anova(fit.model) # ------  se tiver réplicas