Hiptmair–Xu preconditioner
In mathematics, Hiptmair–Xu (HX) preconditioners are preconditioners for solving H ( curl ) {\displaystyle H(\operatorname {curl} )} and H ( div ) {\displaystyle H(\operatorname {div} )} problems based on the auxiliary space preconditioning framework. An important ingredient in the derivation of HX preconditioners in two and three dimensions is the so-called regular decomposition, which decomposes a Sobolev space function into a component of higher regularity and a scalar or vector potential.
Source: Wikipedia — Hiptmair–Xu preconditioner (CC BY-SA 4.0)