Let G be a simple connected graph, and take 0<=i<=d(G), where d(G) is the graph diameter. Then G has global parameters c_i (respectively a_i, b_i) if the number of vertices at distance i - 1 (respectively, i, i + 1) from a given vertex v that are adjacent to a vertex w at distance i from v is the constant c_i (respectively a_i, b_i) depending only on i (i.e., not on v of w).

distance-regular graph | intersection array