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A038379
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Number of real {0,1} n X n matrices A such that M = A + A' has 2's on the main diagonal, 0's and 1's elsewhere and is positive semi-definite.
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5
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OFFSET
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1,2
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COMMENTS
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Necessarily A has all 1's on the main diagonal.
A real matrix M is positive semi-definite if its eigenvalues are >= 0.
For n <= 4, a(n) = the upper bound 3^C(n,2).
For number of different values of A + A' see A085658. - Max Alekseyev, Nov 11 2006
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LINKS
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FORMULA
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Equals Sum_{k=0..C(n,2)} 2^k*T(n,k), where T(n,k) is given by A083029.
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CROSSREFS
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Cf. A055165, which counts nonsingular {0, 1} matrices, A003024, which counts {0, 1} matrices with positive eigenvalues, A085656 (positive definite matrices).
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KEYWORD
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nonn,more,nice
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AUTHOR
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EXTENSIONS
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Definition corrected Nov 10 2006
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STATUS
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approved
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