  This paper is concerned with the Hamiltonian actions of a torus on a
symplectic manifold. We are interested here in two global invariants: the
Duistermaat-Heckman measure DH(M), and the Riemann-Roch chatacters
RR(M,L^k),k>0, which are defined when the symplectic manifold is prequantized
by a Kostant-Souriau line bundle L.
  We can associate to each connected component C of regular values of the
moment map the following local invariants: the polynomial DH_c which coincides
with DH(M) on C, and the periodic polynomial m_c which computes the
multiplicity of RR(M,L^k), k>0, in the cone generated by C.
  The purpose of this paper is to compute the differences DH_c - DH_c' and m_c
- m_c' when C and C' are two adjacent connected components of regular values of
the moment map.
