title: How to store a symmetric matrix?
body: <p>Which is the best way to store a symmetric matrix in memory?</p>
  
  <p>It would be good to save half of the space without compromising speed and complexity of the structure too much. This is a language-agnostic question but if you need to make some assumptions just assume it's a good old plain programming language like C or C++..</p>
  
  <p>It seems a thing that has a sense just if there is a way to keep things simple or just when the matrix itself is really big, am I right?</p>
  
  <p>Just for the sake of formality I mean that this assertion is always true for the data I want to store</p>
  
  <pre><code>matrix[x][y] == matrix[y][x]
  </code></pre>