le function. If omitted, <tt>U.feval(x)</tt>
            only works if the union has a single function.
        </li>
    
      </ul>
    
    
      <b>Outputs</b>
      <br><br>
    
      <ol>
        
         <li> 
            <tt>x</tt> is not contained in any polyhedron of the union:
        
            <tt>fval</tt> = <img src="../../../../../../fig/mpt/modules/geometry/unions/@PolyUnion/feval1.png" alt="../../../../../../fig/mpt/modules/geometry/unions/@PolyUnion/feval1.png"> vector of <tt>NaNs</