[SciPy-user] solve for symetric matrix ?

Ronan Perrussel Ronan.Perrussel@ec-lyon...
Thu Apr 26 08:01:07 CDT 2007


fred a écrit :
> Joachim Dahl a écrit :
>   
>> 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.
> h, I surely misunderstand something but what ?....
>   
ei is a vector of the canonical basis of R^n.
For instance, e1 = (1, 0, ..., 0)' and e1'*A*e1 = A_{11} = 0.
If A is positive definite, it should be stricly positive.

(As you can remark, all the coefficients of your diagonal should be 
strictly positive.)

Ronan

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