Convex Optimization, Convex Sets, Convex Function, Convex Hull, Convexity.
domain D and x satisfies the condition given. To understand this better, lets see the following examples to understand this better: In the first example, S is a set of all x such that x is a natural number and 1 is less or equal to x, which is less than or equal to 5. In the second example, S is a