In mathematics, more precisely in the theory of functions of several complex variables, a pseudoconvex set is a special type of open set in the n-dimensional complex space C<sup>n</sup>. Pseudoconvex sets are important, as they allow for classification of domains of holomorphy.
Let be a domain. One says that is pseudoconvex (or Hartogs pseudoconvex) if there exists a continuous plurisubharmonic function on such that the set is a relatively compact subset of for all real numbers In other words, a domain is pseudoconvex if has a continuous plurisubharmonic exhaustion function. Every (geometrically) convex set is pseudoconvex. However, there are pseudoconvex domains which are not geometrically convex.
When has a (twice continuously differentiable) boundary, this notion is the same as Levi pseudoconvexity, which is easier to work with. More specifically, with a boundary, it can be shown that has a defining function, i.e., that there exists which is so that , and . Now, is pseudoconvex if and only if for every and in the complex tangent space at p, that is,
The definition above is analogous to definitions of convexity in Real Analysis.
If does not have a boundary, the following approximation result can be useful.
Proposition 1 If is pseudoconvex, then there exist bounded, strongly Levi pseudoconvex domains with (smooth) boundary which are relatively compact in , such that
This is because once we have a as in the definition we can actually find a C<sup>âÂÂ</sup> exhaustion function.
In one complex dimension, every open domain is pseudoconvex.