# Solutions to a System of Equations for $C^m$ Functions

## TL;DR

This paper develops algorithms to determine when a system of linear equations with semialgebraic function coefficients has a $C^m$ solution, by identifying a finite set of differential operators that characterize solvability.

## Contribution

It introduces algorithms for computing differential operators that characterize the existence of $C^m$ solutions to systems with semialgebraic coefficients.

## Key findings

- Algorithms for computing differential operators are provided.
- Characterization of solvability via annihilation by differential operators.
- Applicable to systems with semialgebraic function coefficients.

## Abstract

Fix $m\geq 0$, and let $A=\left( A_{ij}\left( x\right) \right) _{1\leq i\leq N,1\leq j\leq M}$ be a matrix of semialgebraic functions on $\mathbb{R}^{n}$ or on a compact subset $E \subset \mathbb{R}^n$. Given $f=\left( f_{1},\cdots ,f_{N}\right) \in C^{\infty }\left( \mathbb{R}^{n},\mathbb{R}^{N}\right) $, we consider the following system of equations \begin{equation} \sum_{j=1}^{M}A_{ij}\left( x\right) F_{j}\left( x\right) =f_{i}\left( x\right) \text{ }\left( i=1,\cdots ,N\right) \text{.} \end{equation} In this paper, we give algorithms for computing a finite list of linear partial differential operators such that $AF= f$ admits a $C^m(\mathbb{R}^n, \mathbb{R}^M)$ solution $F=(F_1,\cdots, F_M)$ if and only if $f=(f_1,\cdots, f_N)$ is annihilated by the linear partial differential operators.