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From: Greg Heath <heath@alumni.brown.edu>
Newsgroups: comp.soft-sys.matlab
Subject: Re: (fsolve) + (Scaling): Possibly Simple Problem - Urgent Help Needed
Date: Thu, 10 Nov 2011 23:01:24 -0800 (PST)
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On Nov 10, 9:19 am, "Alaa Elwany" <alaa_elw...@yahoo.com> wrote:
> Thanks a lot Greg.  I would like to try your scaling suggestion, but I am not sure how I can implement this in my code.  You said "Make the replacement x1 = 1e-23*x3".  Do you mean I should regard x3 and x4 as my variables, solve the equation, then transform back to x1 and x2 after I solve?  Please advise.
>
> Alaa
>
>
>
> Greg Heath <he...@alumni.brown.edu> wrote in message <244944b4-f56a-4312-a540-9c77cc0cb...@c18g2000yqj.googlegroups.com>...
> > On Nov 9, 5:10 pm, "Alaa Elwany" <alaa_elw...@yahoo.com> wrote:
> > > Thank you very much for your response Roger.  However, being familiar with this "Starting Solution" dilemma, I did have a validation problem instance, for which I knew in advance that the solution is x1 = 1.2e-23, x2=8.2   I set the starting solution to:
> > > (1e-23,8.0) --> fsolve stalled, gave no solution and the same error message.
>
> > > It's driving me CRAZY!! Apparently, it is not a problem regarding "a good initial guess", but something else, and this is why I thought of a scaling issue, specially that the error message has to do with "step size".
>
> > > Does this additional (and weird) observation give you a clue to any possible explanation? perhaps there is an alternative solution that I didn't think of?
>
> > > Thank you very much for your concern again, regardless of whether the problem is resolved or not.
>
> > > Alaa
>
> > What happens when you make the replacements x1 = 1e-23*x3 and x2 =
> > 10*x4?
>
> > Hope this helps.
>
> > Greg- Hide quoted text -
>
> - Show quoted text -

Yes.

Please do not TOP-POST.

Put your reply within and/or after the previous post.

HTH.

Greg