On 2/5/10 1:13 PM, Dustin Bortner wrote:
> I'm using wxMaxima 0.8.4 with Maxima 5.20.1. I ran into a problem
> when calling eigenvalues (and so eigenvectors, too):
>
> I am simply trying to get the eigenvalues for a 6x6 Laplacian matrix
> (-R6) :
>
> R6:matrix(
> [-16,10,1,1,3,1],
> [10,-(18),1,2,1,4],
> [1,1,-(2+3*8),8,8,8],
> [1,2,8,-(3+3*8),8,8],
> [3,1,8,8,-(4+3*8),8],
> [1,4,8,8,8,-(5+3*8)]
> );
>
> eigenvalues(-R6);
>
> The last command gives the following:
>
> part: fell off the end.
> #0:
> eigenvalues(mat=matrix([16,-10,-1,-1,-3,-1],[-10,18,-1,-2,-1,-4],[-1,-1,26,-8,-8,-8],[-1,-2,-8,27,-8,-8],[-3,-1,-8,-...)(eigen.mac
> line 94)
> -- an error. To debug this try: debugmode(true);
Thanks for the bug report.
This appears to be a bug in eigenvalues. Eigenvalues computes the
characteristic polynomial and tries to solve it. Solve finds that one
solution is 0, and returns a 5th order polynomial. But eigenvalues
expects that solve either returns [] for no solutions or returns all
solutions.
I think even if we fixed this, eigenvalues would fail to find the
eigenvalues since we can't solve a 5th order polynomial analytically in
general.
Ray