 Closed convex hull

The smallest closed convex set containing a set $C$, equivalently the closure of its convex hull in the specified topology. The topology must be stated: the norm topology, weak topology and weak-star topology need not give the same closure for an arbitrary set.

Even a bounded infinite input need not have a closed convex hull. In the real line, let $S=\{1/n:n\ge 1\}$. Every finite convex combination of these positive points is positive, so zero is absent. Conversely, any $x\in (0,1]$ lies between some $1/n$ and $1$, and is their convex combination. HenceThe closed convex hull adds the missing limit point zero. For the finite eight-point example in convex hull, the convex hull is already closed, so taking the closed convex hull adds nothing.