In rigidity theory a stress (or self-stress) on a framework ${\displaystyle (G,p)}$ assignes to each edge ${\displaystyle e\in E(G)}$ a real number ${\displaystyle \omega _{e}}$.

A stress is an equilibrium stress if at each vertex ${\displaystyle v\in V(G)}$ holds

${\displaystyle \sum _{w\,:\,vw\in E(G)}\!\!\!\!\omega _{vw}(p_{v}-p_{w})=0.}$