[seqfan] Re: seq needed of (0,+-1) matrices

israel at math.ubc.ca israel at math.ubc.ca
Thu Jan 19 22:30:39 CET 2012


Your program is using 
A[w,x]*A[y,z]+A[w,y]*A[x,z]+A[w,z]*A[x,y]-A[w,x]*A[w,y]*A[w,z]*A[x,y]*A[x,z]*A[y,z]

but the original message had

a_wx a_yz + a_wy a_zx + a_wz a_xy = a_wx a_wy a_wz a_xy a_xz a_yz

So should the second term use A[x,z] or A[z,x]? It's likely to make a 
difference.

Robert Israel
University of British Columbia

On Jan 19 2012, N. J. A. Sloane wrote:

>well, I get a(4) = 125 using Maple, agreeing with Max.
>
> Here's my Maple code: with(combinat); A:=Matrix(4,4): for i from 1 to 4 
> do A[i,i]:=0; od: n:=0; for a from -1 to 1 do A[1,2]:=a; A[2,1]:=-a; for 
> b from -1 to 1 do A[1,3]:=b; A[3,1]:=-b; for c from -1 to 1 do A[1,4]:=c; 
> A[4,1]:=-c; for d from -1 to 1 do A[2,3]:=d; A[3,2]:=-d; for e from -1 to 
> 1 do A[2,4]:=e; A[4,2]:=-e; for f from -1 to 1 do A[3,4]:=f; A[4,3]:=-f; 
> perms:=permute(4); nsw:=+1; for i from 1 to 24 do p:=perms[i]; w:=p[1]; 
> x:=p[2]; y:=p[3]; z:=p[4]; 
> star:=A[w,x]*A[y,z]+A[w,y]*A[x,z]+A[w,z]*A[x,y]-A[w,x]*A[w,y]*A[w,z]*A[x,y]*A[x,z]*A[y,z]; 
> if star <> 0 then nsw:=-1; break; fi; od: if nsw = 1 then n:=n+1; fi; od: 
> od: od: od: od: od: n;
>
>Neil
>
>
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