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Re: Problems with fzero

From: John W. Eaton
Subject: Re: Problems with fzero
Date: Thu, 31 Oct 2002 18:44:51 -0600

On 31-Oct-2002, Schloegl Alois <address@hidden> wrote:

| x=-10:.001:10;
| y=x-1.09-2.7217*log(1+(x/2.7217));
| plot(x,real(y'*[1,-i]))
| Based on this graph, the solutions 3.2106 and -1.7701 are correct. 
| for all x<2.7217, y(x) is complex. It looks like FZERO (and FSOLVE) look only 
| for the real part of the function y(x). If y(x) has a non-zero imaginary 
| a warning (or error) message should appear.

Yes, if you are using fsolve and one of the sampled values of your
function is complex, Octave should print

  warning: implicit conversion from complex scalar to real matrix

In the next development snapshot, Octave will also print

  warning: fsolve: ignoring imaginary part returned from user-supplied function

the first time this happens on any given call to fsolve.


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