Two-party graphs and monotonicity properties of the Poincaré mapping

The local differential of a system of nonlinear differential equations with a $T$-periodic right-hand side is representable as a directed sign interaction graph. Within the class of balanced graphs, where all paths between two fixed vertices have the same signs, it is possible to estimate the sign structure of the differential of the global Poincaré mapping (a shift in time $T$). In this case all vertices of a strongly connected graph naturally break into two sets (two parties). As appeared, the influence of variables within one party is positive, while that of variables from different parties is negative. Even having simplified the structure of a local two-party graph (by eliminating its edges), one can still exactly describe the sign structure of the differential of the Poincare mapping. The obtained results are applicable in the mathematical competition theory.