/// Evaluate the coefficient virtual double Eval(ElementTransformation &T, const IntegrationPoint &ip) { return pow(a->Eval(T, ip), p); }
virtual double Eval(ElementTransformation &T, const IntegrationPoint &ip) { return active_attr[T.Attribute-1] ? c->Eval(T, ip, GetTime()) : 0.0; }
/// Evaluate the coefficient virtual double Eval(ElementTransformation &T, const IntegrationPoint &ip) { return alpha * a->Eval(T, ip) + beta * b->Eval(T, ip); }