Semialgebraic ${C^m}$ solutions to a univariate system of linear inequalities with Nash forcing

Source abstract

Let $(A_{ij}(x))_{1 \leq i \leq N, 1 \leq j \leq M}$ be a matrix of univariate semialgebraic functions. We study the solvability of the system of linear inequalities $$\begin{equation*} \sum_{j=1}^M A_{ij}(x)F_j(x)\leq f_i(x) \ \ \text{ for } i = 1, \ldots, N, \end{equation*}$$ where we assume each forcing $f_i$ is a Nash function. We show that the $C^m$ solvability of the system can be characterized by finitely many linear ordinary differential inequalities in $f$ with semialgebraic coefficients depending only on $(A_{ij})$. When the system is solvable, the solution may be chosen semialgebraic, and the proof gives a constructive procedure in the semialgebraic sense. We also study the semimodule structure of admissible forcings, establishing finite generation and lack thereof in various settings.