  In this paper we are interested in developments of elliptic functions of
Jacobi. In particular a trigonometric expansion of the classical theta
functions introduced by the author (Algebraic methods and q-special functions,
Editors: C.R.M. Proceedings and Lectures Notes, A.M.S., vol 22, Providence,
1999, 53-57) permits one establish a differential system. This system is
derived from the heat equation and is satisfied by their coefficients. Several
applications may be deduced. Other types of expansions for the Jacobi elliptic
functions as well as for the Zeta function are examined.
