@Override public String toString(){
  StringBuilder result=new StringBuilder("EQUATIONS:\n");
  Enumeration<GraphNode> v=equations.enumerateNodes();
  for (int i=0; i < equations.numberOfNodes(); i++) {
    result.append(i);
    result.append(" : ");
    result.append(v.nextElement());
    result.append('\n');
  }
  return result.toString();
}

@ Override public String toString ( ) { StringBuilder result = new StringBuilder ( "EQUATIONS:\n" ) ; Enumeration < GraphNode > v = equations . enumerateNodes ( ) ; for ( int i = 0 ; i < equations . numberOfNodes ( ) ; i ++ ) { result . append ( i ) ; result . append ( " : " ) ; result . append ( v . nextElement ( ) ) ; result . append ( '\n' ) ; } return result . toString ( ) ; }
return a string representation of the system
