title: what does "Attempt to reference field of non-structure array" error mean?
body: <p>hi do you have any idea what does it mean? and how can I fix it</p>
  
  <pre><code>??? Attempt to reference field of non-structure array.
  Error in ==&gt; sym.symsum at 74
     r = mupadmex('symobj::map',f.s,'symobj::symsum',x.s,a.s,b.s);
  is it about my symbols which are
  
  syms x y Mi q B alp
  </code></pre>
  
  <p>or summation of series...</p>
  
  <p>Probably not easy to answer it with this insufficient information but my whole function consist multiple functions so not easy to introduce here...</p>
  
  <p>And the last question is that is there any difference b/w</p>
  
  <pre><code>syms x &amp; x=sym('x')
  </code></pre>