# Equivalence relations on strongly regular graphs with same parameters

Let $\mathcal{S}$ be the set of all strongly regular graphs with parameter $(n, k, \lambda, \mu)$. Are there any (interesting) equivalence relations defined on this set?

My motivation is to approach isomorphism partition (equivalence relation is being isomorphic) via other coarser partition.

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You can imagine any number of equivalence relations on graphs: via chromatic number, clique number, isomorphism, etc. They seem to remain as interesting on this particular restricted set. – Lev Reyzin Dec 25 '12 at 5:28
I am interested in equivalence relation which can be computed in polynomial time AND induce a partition coarser than isomorphism partition. – DurgaDatta Dec 26 '12 at 8:27