  The compactification of five dimensional N=2 SUSY Yang-Mills (YM) theory onto
a circle provides a four dimensional YM model with N=4 SUSY. This supersymmetry
can be broken down to N=2 if non-trivial boundary conditions in the compact
dimension, \phi(x_5 +R) = e^{2\pi i\epsilon}\phi(x_5), are imposed on half of
the fields. This two-parameter (R,\epsilon) family of compactifications
includes as particular limits most of the previously studied four dimensional
N=2 SUSY YM models with supermultiplets in the adjoint representation of the
gauge group. The finite-dimensional integrable system associated to these
theories via the Seiberg-Witten construction is the generic elliptic
Ruijsenaars-Schneider model. In particular the perturbative (weak coupling)
limit is described by the trigonometric Ruijsenaars-Schneider model.
