Classical r-matrices and compatible Poisson brackets for coupled KdV systems

The formalism of classical r-matrices is used to construct families of compatible Poisson brackets for some nonlinear integrable systems connected with Virasoro algebras. We recover the coupled KdV 1] and Harry Dym 2] systems associated with the auxiliary linear problem 1 $$\sum\limits_{i = 0}^N {\lambda '\left( {a_i \frac{{{\text{d}}^{\text{2}} }}{{{\text{dx}}^2 }} + {\text{u}}_{\text{i}} } \right)} \psi = 0$$ .