ension of the vector <tt>x</tt> must be the same as the dimension of the <tt>PolyUnion</tt>.
        If the point lies outside of the union, the result is <tt>NaN</tt>.
        
    Notes:<br><br>
    
      <ul>
        
         <li> 
            <tt>U</tt> must be a single union. Arrays of unions are not accepted. Use
            <tt>array.forEach(@(e) e.feval(...))</tt> to evaluate arrays of unions.
        </li>
        
         <li>
            
            <tt>function_name</tt> must refer to a sing