Let Γ=(X,R) be a distance-regular graph of diameter d. A parallelogram of length i is a 4-tuple xyzw consisting of vertices of Γ such that ∂(x,y)=∂(z,w)=1, ∂(x,z)=i, and ∂(x,w)=∂(y,w)=∂(y,z)=i−1. A subset Y of X is said to be a completely regular code if the numbers pi,j=|Gj(x)ÇY| (i,j Î {0,1,¼,d})pi_{i,j}=|Gamma_{j}(x)cap Y|quad (i,jin {0,1,ldots,d})
展开▼
