By finding an appropriate eigenvector, show that there is no distance- regular graph with intersection array $\left \{ 3, 2, 1; 1,1, 3 \right \}$.
can you little help me how should I make an eigenvector for the cause,and after I make this,what is its relation with intersection array?
I am confused about this,
any hint or Idea will be great ,thanks.
this is exercise 3.17 page 101 of An Introduction to the Theory of Graph Spectra DRAGOS CVETKOVIC and PETER ROWLINSON and there is no more detailes.