title: Alter identifier names with macros in gams
body: <p>I have multiple parameters named in the same convention, e.g.</p>
  <pre><code>parameter
  par_1_1 /1/
  par_1_2 /2/
  par_2_1 /3/
  par_2_2 /4/
  ;
  </code></pre>
  <p>I want to define a macro, which will be replaced (based on the input) by the identifier, e.g.</p>
  <pre><code>$macro f(x) (x_1_1) 
  </code></pre>
  <p>and use it in my program, e.g.</p>
  <pre><code>variable x;
  x.lo = -1000;
  x.up = 1000;
  
  $macro f(x) (x_1_1)
  
  parameter
  par_1_1 /1/
  par_1_2 /2/
  par_2_1 /3/
  par_2_2 /4/
  ;
  variable obj; equation eqobj; eqobj.. obj =e= x;
  equation eqcon; eqcon.. x =l= f3(par);
  
  
  model mod /all/;
  solve mod minimizing obj using minlp;
  </code></pre>
  <p>Unfortunaly, this is not working because gams will consider <code>x_1_1</code> as an (undefined) symbol.
  Is there any way to accomplish this?</p>