A family of S-mKdV hierarchy of equations and its expanding integrable models

Starting from a subalgebra of loop algebra (A) over tilde (1) we construct a linear isospectral problem. A type of Liouville integrable system and its bi-Hamiltonian structure are presented by the use-of Tu-model again. The reductions to the integrable system give rise to the well-known Schrodinger equation and mKdV equation. Therefore, the system is called S-mKdV hierarchy. In terms of the subalgebra of (A) over tilde (1), constructed, we also construct a new subalgebra (G) over tilde of loop algebra (A) over tilde (2), with five dimensions, from which a linear isospectral form is designed. Again, using Tu-model one obtains a type of expanding integrable models of the S-mKdV hierarchy. Some expanding integrable models of hierarchies, such as BPT hierarchy, TB hierarchy etc. are also obtained by using this method. Hence, the method proposed in this paper has important applications generally. Finally as special cases, the integrable couplings of the well-known Schrodinger equation and mKdV equation are obtained.