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A087488
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Number of n X n (-1,1)-matrices with all eigenvalues >= 0.
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0
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OFFSET
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0,3
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LINKS
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Table of n, a(n) for n=0..4.
B. D. McKay, F. E. Oggier, G. F. Royle, N. J. A. Sloane, I. M. Wanless and H. S. Wilf, Acyclic digraphs and eigenvalues of (0,1)-matrices, J. Integer Sequences, 7 (2004), #04.3.3.
B. D. McKay, F. E. Oggier, G. F. Royle, N. J. A. Sloane, I. M. Wanless and H. S. Wilf, Acyclic digraphs and eigenvalues of (0,1)-matrices
Index entries for sequences related to binary matrices
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EXAMPLE
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For n = 2 the six matrices are (+ means +1, - means -1):
++ +- -- -+ +- ++
-- +- ++ -+ -+ ++
with eigenvalues
00 00 00 00 20 20 respectively.
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CROSSREFS
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Cf. A086510, A003024, A055165, A085656.
Sequence in context: A156887 A173500 A141008 * A179879 A099343 A189509
Adjacent sequences: A087485 A087486 A087487 * A087489 A087490 A087491
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KEYWORD
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nonn,more
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AUTHOR
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Frederique Oggier (frederique.oggier(AT)epfl.ch) and N. J. A. Sloane, Oct 24 2003
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STATUS
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approved
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