title: MathProg out of domain
body: <p>I need to solve a problem using GLPK and what Actually I need is to calculate the difference between elements in two arrays 
  but, I receive error out of domain 
  I hope that you can fix it as I've no idea about this error
  here's the  code</p>
  
  <pre><code>set cols1;
  set cols2;
  set w;
  set range:=1..2;
  #set Groups;
  #set Items{Groups} ;
  param p1{cols1}&gt;=0;
  param p2{cols2}&gt;=0;
  param uf{w}&gt;=0;
  var x&gt;=0;
  maximize regret: x;
  s.t. a: sum { i in range } (p1[i] -p2[i]) * uf[i]&gt;=x;
  s.t. b: sum { i in range } p2[i] * uf[i] =1;
  data;
  set cols1:=40  110;
  set cols2:=51 134;
  set w:= 0.8 0.2;
  #set Groups := {cols1, cols2, w};
  end;
  </code></pre>