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A055548
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Number of normal n X n (-1,1)-matrices.
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3
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OFFSET
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1,1
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COMMENTS
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REFERENCES
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W. H. Press et al., Numerical Recipes, Cambridge, 1986; Chapter 11.
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LINKS
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PROG
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(PARI) NormaQ(a, n) = { my(aT) ; aT=mattranspose(a) ; return( a*aT == aT*a ); }
combMat(no, n) = { my(a, noshif) ; a = matrix(n, n) ; noshif=no ; for(co=1, n, for(ro=1, n, if( (noshif %2)== 1, a[ro, co] = 1, a[ro, co] = -1) ; noshif = floor(noshif/2) ; ) ) ; return(a) ; }
{ for (n = 1, 10, count = 0; a = matrix(n, n) ; for( no=0, 2^(n^2)-1, a = combMat(no, n) ; count += NormaQ(a, n) ; /* if(no%1000==0, print(n, " ", (no/2^(n^2)+0.), " ", count)) ; */ ) ; print(count) ; ) } \\ R. J. Mathar, Mar 14 2006
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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