title: MATLAB: sym function does not works
body: <p>In matlab I want to create symbolic vector:</p>
  
  <pre><code>X = sym(['x_n' 'x_(n-1)' 'x(n-2)'])
  </code></pre>
  
  <p>however, I get</p>
  
  <pre><code>??? Error using ==&gt; sym.sym&gt;expression2ref at 2408
  Error: Unexpected 'identifier' [line 1, col 11]
  
  Error in ==&gt; sym.sym&gt;char2ref at 2378
      s = expression2ref(x);
  
  Error in ==&gt; sym.sym&gt;tomupad at 2147
          S = char2ref(x);
  
  Error in ==&gt; sym.sym&gt;sym.sym at 102
                  S.s = tomupad(x,'');
  </code></pre>
  
  <p>if I try create, e.g. just <code>X = sym(['x_n' 'x_(n-1)'])</code>, it's ok, so what's wrong?</p>