title: Define global constant in Matlab
body: <p>I want to define SI global prefixes in Matlab to make my code self explaining.</p>
  
  <p>I defined it in <code>startup.m</code>:</p>
  
  <pre><code>% define SI prefix
  global SI
  SI.milli = 1e-3;
  SI.micro = 1e-6;
  % and so on..
  </code></pre>
  
  <p>It works fine, if I run <code>test.m</code> directly </p>
  
  <pre><code>% test.m file
  Area = 10 * SI.micro * 4 * SI.milli % m^2
  </code></pre>
  
  <p>But it fails in external functions. How can I make <code>SI</code> visible in the name space of external functions too?</p>