title: Cholesky Decomposition in the rmvnorm package
body: <p>Why is it possible to create non-singular normal random vectors by a covariance matrix which is not positive definite? e.g. its not possible to execute <code>chol(V)</code>.  </p>
  
  <pre><code>pigeon&lt;-data.frame(response=c(10,19,27,28,9,13,25,29,4,10,20,18,5,6,12,17),
                 treatment=factor(rep(1:4,4)),
                 subject=factor(rep(1:4,each=4))
                 )
  m&lt;-dcast(pigeon,subject~treatment, value.var="response")
  fit&lt;-lm(as.matrix(m[,-1])~1)
  V&lt;-cov(residuals(fit))
  eigen(V)$values
  rmvnorm(mean=rep(0,4),sigma=V,n=subject,method="chol")
  </code></pre>