title: Summing up till a certain interval
body: <p>How can I compute the summation of an interval. I will use Matlab's code for eg.</p>
  
  <pre><code>data=[1;2;3;4;5;6;7;8;9;10;11;12]
  </code></pre>
  
  <p>I would like to perform this summation.</p>
  
  <pre><code>sum(1)=data(1)+data(2)+data(3)
  sum(2)=data(4)+data(5)+data(6)
  sum(3)=data(7)+(data(8)+data(9)
  sum(4)=data(10)+data(11)+data(12)
  </code></pre>
  
  <p>How can I get about this? (Using for loop)</p>