/// <summary>
 /// Constructor
 /// </summary>
 /// <param name="numer">Polynomial expression for numerator</param>
 /// <param name="denom">Polynomail expression for denomenator</param>
 public PolyExpression(Polynomial numer, Polynomial denom)
 {
     numerator   = numer;
     denomenator = denom;
 }
 /// <summary>
 /// Constructor to create and empty expression
 /// </summary>
 public PolyExpression()
 {
     numerator   = new Polynomial();
     denomenator = new Polynomial();
 }