Hi,
(%i6) M;
(%o6) matrix([0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4],[1,0,2,1,2,1,3,2,2,1,3,2,3,2,4,3],
[1,2,0,1,2,3,1,2,2,3,1,2,3,4,2,3],[2,1,1,0,3,2,2,1,3,2,2,1,4,3,3,2],
[1,2,2,3,0,1,1,2,2,3,3,4,1,2,2,3],[2,1,3,2,1,0,2,1,3,2,4,3,2,1,3,2],
[2,3,1,2,1,2,0,1,3,4,2,3,2,3,1,2],[3,2,2,1,2,1,1,0,4,3,3,2,3,2,2,1],
[1,2,2,3,2,3,3,4,0,1,1,2,1,2,2,3],[2,1,3,2,3,2,4,3,1,0,2,1,2,1,3,2],
[2,3,1,2,3,4,2,3,1,2,0,1,2,3,1,2],[3,2,2,1,4,3,3,2,2,1,1,0,3,2,2,1],
[2,3,3,4,1,2,2,3,1,2,2,3,0,1,1,2],[3,2,4,3,2,1,3,2,2,1,3,2,1,0,2,1],
[3,4,2,3,2,3,1,2,2,3,1,2,1,2,0,1],[4,3,3,2,3,2,2,1,3,2,2,1,2,1,1,0])
(%i7) charpoly(M,x);
This runs now already for a day!
Computing the characteristic polynomial is somewhat more expensive than Gaussian
elimination, but not too much, and so I believe something is wrong here.
Oliver