Abstract. Assume K ⊂ R d is a convex body and X is a (large) finite subset of K. How many convex polytopes are there whose vertices belong to X? Is there a typical shape of such polytopes? How well does the maximal such polytope (which is actually the convex hull of X) approximate K? We are interested in these questions mainly in two cases. The first is when X is a random sample of n uniform, independent points from K. In this case motivation comes from Sylvester's famous four-point problem and from the theory of random polytopes. The second case is when X = K ∩ Z d where Z d is the lattice of integer points in R d and the questions come from integer programming and geometry of numbers. Surprisingly (or not so surprisingly), the answers in the two cases are rather similar.
Sylvester's four-point problemThe study of random points in convex bodies started with an innocent looking question. The year was 1864. The place was London. The journal was the Educational Times. Problem 1941 came from J. J. Sylvester [60]. It read: "Show that the chance of four points forming the apices of a reentrant quadrilateral is 1/4 if they be taken at random in an indefinite plane." Several answers came in. Most of them were different. In 1865 Sylvester [61] concluded, "This problem does not admit of a determinate solution." The reason is, as we all know by now, in "at random in an indefinite plane", since there is no natural probability measure on it. Sylvester immediately modified the question: Let K be a convex body in the plane and choose four random, independent, and uniform points from K. What is the probability that they form the vertices of a reentrant quadrilateral, or, in recent terminology, that their convex hull is a triangle. Further, for what K is this probability the smallest and the largest.This question has become known as Sylvester's four-point problem, and it has proved to be extremely fertile. It took more than fifty years (and several erroneous proofs) to find the answer. Blaschke showed in [26] and [27] that the probability in question is largest for a triangle and smallest for the disk (or any ellipse). His solution used the method of symmetrization and "shaking down" that have become standard tools since.Sylvester's question, and its subsequent solution, determined the direction of research for a long time. Many papers have been written starting with the setting: Let X n = {x 1 , ..., x n } be a random, independent, uniform sample of n points from