Static class-guided selection of elementary solutions in non-monotone vanishing discount problems

We study a generalized vanishing discount problem for Hamilton–Jacobi equations, removing the standard monotonicity assumption, either in a global sense or when integrated against all Mather measures. Specifically, we consider $$\lambda a(x)u(x)+H(x,Du(x))-A\lambda =c_0,$$ with a suitably chosen constant $A>0$. By appropriately changing the signs of the function $a(x)$ on different static classes associated with $H$, we show that the maximal viscosity solution converges uniformly as $\lambda \to 0^{+}$ and that all elementary solutions of the stationary equation $$H(x,Du(x))=c_0$$ can be selected as limits. This provides the first result for selecting multiple viscosity solutions in vanishing discount problems beyond the usual monotonicity and integral assumptions, as long as $a(x)$ is positive on one static class. Our results highlight the crucial role of static classes in controlling the asymptotic behavior of viscosity solutions. Previously, under usual monotonicity assumptions, only a single solution could be selected (as discussed in \cite{GL}), whereas our approach allows controlled selection of multiple solutions via static class-guided discount coefficients.