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Re: fsolve features

From: Thomas Walter
Subject: Re: fsolve features
Date: Thu, 15 Jul 1999 10:32:06 +0200

>>>>> "John" == John W Eaton <address@hidden> writes:

    John> On  5-Jul-1999, Rolf Fabian <address@hidden> wrote a number of
    John> complaints about Octave's fsolve function including

    John>   * fsolve is not able to compute complex-valued solutions.

    John>   * fsolve discards the imaginary part of complex-valued initial 

    John>   * fsolve discards the imaginary part of complex-valued function
    John>     evaluations.

    John> Note that warnings about discarding the imaginary part of a complex
    John> value are given by default, but may be suppressed depending on the
    John> setting of the built-in variable ok_to_lose_imaginary_part.

In some cases it helps to write the function in a way to return two
real solutions instead of a  one complex solution. Something similar
can be done for the parameters, but ...

    John> The problem is that fsolve is not intended to handle complex-valued
    John> functions or find complex-valued solutions.  It is based on Minpack's
    John> hybrd function, which is only good finding real-valued solutions for
    John> real-valued functions.

... adding support for complex values would be a big step forward.

And what about the other methods from minpack?  For example the
interfaces to some least square fitting function which are derived
from LEvenberg-Marqurdt methods?  Having fitting functions would be
really nice!  But I don't speak fortran.

    John> If you have a better solution, please consider providing it as an
    John> alternative (submit it to octave-sources, for starters).  If it is
    John> really better, then perhaps it can become the default method for
    John> fsolve.

    John> Thanks,

    John> jwe

Any hints to solve and fit complex valued function are welcome.


Der dauerhafte Zustand eines Luftballons.

Dipl. Phys. Thomas Walter
Inst. f. Physiklische Chemie II
Egerlandstr. 3                          Tel.: ++9131-85 27326 / 27330
91058 Erlangen, Germany                 email: address@hidden

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