title: Simplifying a very long symbolic expression by automatically introducing temporal variables or in any other way
body: <p>After attempting to solve a symbolic math problem, I got an expression with about 17000 characters. I am using the symbolic toolbox for Matlab, but I am open to any suggestion (Mathematica, whatever).</p>
  
  <p>For obvious reasons, I won't copy-paste the expression straight into the question. <a href="https://raw.github.com/gist/1702842/8aff11800e42140dd76265d288a1f4b4dc5ea995/gistfile1.txt">Here is a link instead</a>.</p>
  
  <p>Running the <code>Matlab</code> commands <code>simplify</code> and <code>simple</code>, and even attempts to <code>collect</code> didn't improve the situation (Some got it worse).</p>
  
  <p>But I am wondering, I don't care if the expression is evaluated in steps, with temporal parameters. Something like:</p>
  
  <pre><code> z1 = a^2*y1;
   %Now the expression can be simplified by using z1 as alias!
   z1+z1^2 ....
  </code></pre>
  
  <p>Is there an automatic method to get such a step-by-step simplification with temporal variables? Also, any other method that you can think of is plausible.</p>