title: Matrix -> blocks division
body: <p>I want to load some matrix into my program and then I want to divide it into smaller blocks.
  What I want exactly can be seen on an image below:</p>
  
  <p><a href="http://postimg.org/image/aki19hjx9/ba463111/" rel="nofollow">http://postimg.org/image/aki19hjx9/ba463111/</a></p>
  
  <p>In red squares are 3 examples of my "blocks" in which I would like to divide whole matrix. In this case each block should be (smaller) 3x3 matrix. I know how to load it into 2d array, but what should I do then?</p>