[SciPy-user] solve for symetric matrix ?

Joachim Dahl dahl.joachim@gmail....
Thu Apr 26 06:40:11 CDT 2007


On 4/26/07, Nils Wagner <nwagner@iam.uni-stuttgart.de> wrote:
>
> Joachim Dahl wrote:
> >
> >
> > On 4/26/07, *fred* <fredmfp@gmail.com <mailto:fredmfp@gmail.com>> wrote:
> >
> >     Hi,
> >
> >     I use scipy.linalg.solve() to solve Au=b, where A is symetric (and
> >     diagonal filled with 0).
> >
> >
> > If the diagonal is 0, then the matrix is not definite (so, neither is
> > -A)...
> >
> >
> >
> I missed the main information (zero diagonal)
> Are you aware of a simple proof that a symmetric matrix with zero
> diagonal entries is indefinite ?


if diag(A)=0 then   ei'*A*ei  = 0 so A is not positive definite.  Same goes
for -A,  so A is
not negative definite either.
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