title: find blue estimator of linear model in R
body: <p>I have the following linear model, and I'd want to find the Best linear unbiased estimator</p>
  
  <pre><code>x&lt;-c(rep(c(1,0,-1,0),4),rep(c(0,1,0,-1),4),rep(c(1,1,0,0),4), rep(c(2,2,-1,-1),4))
  x&lt;-matrix(x,ncol=4,byrow=T) 
  y&lt;-c(2.1,1.9,2,2.2,1.2,0.8,1.1,0.9,5.1,5.2,4.9,4.9,7.9,8,8.2,7.9)
  </code></pre>