Ill-Posed
A partial differential equation is ill-posed if its solution does not depend continuously on its parameters, including but not limited to boundary conditions.
See also
Ill-DefinedExplore with Wolfram|Alpha
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Cite this as:
Weisstein, Eric W. "Ill-Posed." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Ill-Posed.html