title: Matlab simplify - why does it remove fractions?
body: <p>I am recently working with Matlab's <code>Symbolic Toolbox</code>, but encountered a big problem. I have some example code:   </p>
  
  <pre><code>syms s w;
  G = 0.1253/(s^4 + 0.5816*s^3 + 1.1691*s^2 + 0.4048*s + 0.177)
  L1=diff(G)
  L2=subs(L1,s,-s)
  M2=subs(G,s,-s)
  Ts=(-1/2)*((L1/G)+(L2/M2))
  T=subs(Ts,s,1i*w)
  Ts = simplify(T)
  </code></pre>
  
  <p>Everything is working well, except for the part with <code>T=subs(Ts,s,1i*w)</code> and <code>T=subs(Ts,s,1i*w)</code>. In order to calculate <code>i</code> as <code>i^2 = -1</code>, I have to use <code>simplify</code>, but then all of the fractions disappear.</p>
  
  <p>Is there any other function to do what I need? Or am I doing something wrong?</p>