Abstract. Let G be a finite group of order v. A k-element subset D of G is called a (v, k, 3,,/z)-partial difference set if the expressions gh -1, for g and h in D with g ~ h, represent each nonidentity element in D exactly ), times and each nonidentity element not in D exactly # times. If e t~ D and g E D iff g-1 E D, then D is essentially the same as a strongly regular Cayley graph. In this survey, we try to list all important existence and nonexistence results concerning partial difference sets. In particular, various construction methods are studied, e.g., constructions using partial congruence partitions, quadratic forms, cyclotomic classes and finite local rings. Also, the relations with Schur tings, two-weight codes, projective sets, difference sets, divisible difference sets and partial geometries are discussed in detail.
Strongly Regular Graphs and Partial Difference SetsA graph I TM with v vertices is said to be a (v, k, k, #)-strongly regular graph if (i) it is regular of valency k, i.e., each vertex is joined to exactly k other vertices; (ii) any two adjacent vertices are both joined to exactly 3, other vertices and two nonadjacent vertices are both joined to exactly/z other vertices. A Cayley graph is defined as a graph r = (v, E) which admits an automorphism group G acting regularly on the vertex set V (see Yap [7] for background on Cayley graphs). If we identify the vertices of I ~ with the elements of the regular automorphism group G, then r can be generated by a subset D of G such that two vertices g, h E G are joined nonabelian) if the group G is abelian (resp. nonabelian). For a subset S of a group G, let S it) = {g~ : g E S} for any integer t.