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Re: MPfit question [message #62731 is a reply to message #62623]

Thu, 02 October 2008 08:59

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

Wox <nomail@hotmail.com> writes:
>
> Ah yes, I see now. Thanks for your comments. I must say it's quite an
> impressive and complicated piece of code. I'm having a hard time
> understanding the convergence criteria and the calculation of the
> LM-step. Can you recommend some reference where I can find more
> details? I sure have some books explaining NLLS-refinement but they
> don't seem to mention some of the criteria I see in your code. Also
> the calculation of the LM-step is done differently each time I open a
> new book :-).

Hi, the code is based on MINPACK-1, so the convergence criteria come
from that library. The references section of mpfit.pro contains two
citations by one of the primary authors of MINPACK. Unfortunately
they are hard to find. :-(

I am suspecting that for your problem, MPFIT is claiming the problem
converged when it didn't, if the "actual" change in chi^2 is much
smaller than "predicted". The only real way I can see this happening
is if you started a parameter *very close* to a boundary but not
exactly on the boundary. The fix for that should be obvious.

Craig

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Craig B. Markwardt, Ph.D. EMAIL: cbmarkwardt+usenet@gmail.com
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[Message index]

		MPfit question By: Wox on Tue, 30 September 2008 07:38
		Re: MPfit question By: Craig Markwardt on Thu, 02 October 2008 08:59
		Re: MPfit question By: Wox on Thu, 02 October 2008 04:39
		Re: MPfit question By: Craig Markwardt on Wed, 01 October 2008 10:16
		Re: MPfit question By: Wox on Wed, 01 October 2008 01:31
		Re: MPfit question By: Craig Markwardt on Tue, 30 September 2008 08:49
		Re: MPFIT question By: Craig Markwardt on Tue, 13 January 2009 22:41
		Re: MPFIT question By: j.coenia@gmail.com on Wed, 14 January 2009 07:54
		Re: MPFIT question By: j.coenia@gmail.com on Thu, 15 January 2009 08:17
		Re: MPFIT question By: Craig Markwardt on Fri, 16 January 2009 22:10
		Re: MPFIT question By: Craig Markwardt on Wed, 14 January 2009 23:52
		Re: MPFIT question By: pgrigis on Wed, 14 January 2009 14:08
		Re: MPFIT question By: j.coenia@gmail.com on Wed, 14 January 2009 13:37
		Re: MPFIT question By: Craig Markwardt on Wed, 14 January 2009 08:23

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