title: What is a parity check matrix? (Information theory)
body: <p>I'm studying information theory but one thing I can't seem to work out.</p>
  
  <p>I know that given a linear code C and a generator matrix M I can work out all the possible codewords of C.</p>
  
  <p>However I do not understand:</p>
  
  <ul>
  <li>What a parity check matrix is <a href="http://en.wikipedia.org/wiki/Parity-check_matrix" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Parity-check_matrix</a></li>
  <li>How to make a parity check matrix from a generator matrix</li>
  </ul>
  
  <p>I'd really appreciate any pointers!</p>
  
  <p>Thanks!</p>