[SciPy-user] det(A-\lambda B) is identically zero
Pearu Peterson
pearu at scipy.org
Fri Feb 13 07:56:15 CST 2004
On Fri, 13 Feb 2004, Nils Wagner wrote:
> Please find attached a small example for a singular pencil
> A-\lambda B. det(A-\lambda B) is identically zero.
> However linalg.eig(A,B) computes certain eigenvalues.
And one of them is inf. That should make an user careful
when manipulating with (A,B) eigendata.
> although \lambda can be chosen arbitrarely.
Well, if lambda is small then det is close to small number indeed.
However note that
>>> linalg.det(A-1e5*B)
-966.29150970670446
for instance.
> There should be at leat a warning in such a case.
I think it is a computer numerics issue rather than of scipy.
What would be the criterion when such a message should be displayed?
Pearu
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