title: elementary R matrices
body: <p>Playing around while trying to refresh my R "knowledge" I did this</p>
  
  <pre><code>&gt; a &lt;- matrix(1:20, byrow=TRUE, nrow = 4)
  &gt; a
       [,1] [,2] [,3] [,4] [,5]
  [1,]    1    2    3    4    5
  [2,]    6    7    8    9   10
  [3,]   11   12   13   14   15
  [4,]   16   17   18   19   20
  &gt; b &lt;- a[3:4, 1:2]
  &gt; b
       [,1] [,2]
  [1,]   11   12
  [2,]   16   17
  &gt; c &lt;- matrix(b, byrow = TRUE, nrow = 2)
  &gt; c
       [,1] [,2]
  [1,]   11   16
  [2,]   12   17
  </code></pre>
  
  <p>Why is <code>c</code> different from <code>b</code>? What happens under the hood?</p>