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Re: Problems with fzero


From: Schloegl Alois
Subject: Re: Problems with fzero
Date: Thu, 31 Oct 2002 19:24:18 +0100 (MET)
User-agent: IMP/PHP IMAP webmail program 2.2.8

see

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 part, 
a warning (or error) message should appear.

    Alois 



Zitiere Diego Ruiz Moreno <address@hidden>:

> Hello all,
>     I have a BIG problem with fzero
>     I have a "strange" function that is y =
> x-1.09-2.7217*log(1+(x/2.7217));
>     When I ask to fzero with a positive initial numbre, let X0= 5, the 
> answer is correct, it is 3.2106, but if I give an negative initial point
> 
> (-1) the answer is -1.7701 That is not correct, and more if I call  it 
> with -5 tyhe answer is -3.2701, and finally if I call it with -51the 
> aswer is correct.
>     Could somebody explain to me this behavior ??
> 
>     Thanks.
> 
> Diego
>  
> 
> 
> 
> 
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