= Strict ellipticity
{title2=$\xi^TA(x)\xi>0\quad(\xi\ne0)$}
For a real <symmetric matrix> field $A$, strict ellipticity means that $A(x)$ is a <positive-definite matrix> at every point. Continuity makes its smallest <eigenvalue> positive uniformly on each <compact subset> of the domain. A uniform positive lower bound on the entire domain is the stronger <uniform ellipticity> condition. Some conventions include a finite uniform upper bound in the latter term, while others state coefficient boundedness separately.
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