On the Multiplicities of the Primitive Idempotents of a Q-Polynomial Distance-regular Graph |
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Authors: | Q |
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Institution: | Department of Mathematics, De La Salle University-Manila, Manila, Philippinesf1 |
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Abstract: | Ito, Tanabe and Terwilliger recently introduced the notion of a tridiagonal pair. We apply their results to distance-regular graphs and obtain the following theorem.Theorem Let Γ denote a distance-regular graph with diameter D ≥ 3. Suppose Γ is Q -polynomial with respect to the orderingE0 , E1, , EDof the primitive idempotents. For 0 ≤ i ≤ D, let midenote the multiplicity ofEi . Then (i)mi − 1 ≤ mi (1 ≤ i ≤ D / 2),(ii)mi ≤ mD − i (0 ≤ i ≤ D / 2).By proving the above theorem we resolve a conjecture of Dennis Stanton. |
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