[Numpy-discussion] roots and high-order polynomial

Fabrice Silva silva@lma.cnrs-mrs...
Mon Jul 6 13:33:31 CDT 2009

Le lundi 06 juillet 2009 à 17:57 +0200, Fabrice Silva a écrit :
> Le lundi 06 juillet 2009 à 17:13 +0200, Nils Wagner a écrit :
> > IIRC, the coefficients of your polynomial are complex.
> > So, you cannot guarantee that the roots are complex 
> > conjugate pairs.
> Correct! If the construction is done with X1 and X1* treated separately,
> the coefficients appear to be complex. But if their processing is done
> simultaneously, the combination gives real coefficients. Let me modify
> this point and come back to tell you if it is the breakpoint...

Alright, the coefficients are now all real (I still wonder how it passed
the check tests I have).

You can find attached a simple test. Looking at the evolution of a.r, it
seems there really is a trouble with the representation of high order
polynomial. 'a' is initialized with its roots, but a.r is far from equal
to the input roots...
Fabrice Silva
Laboratory of Mechanics and Acoustics - CNRS
31 chemin Joseph Aiguier, 13402 Marseille, France.
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