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Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? [message #52883]

Thu, 08 March 2007 07:53

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

Wox wrote:
> On 07 Mar 2007 21:07:36 -0500, Craig Markwardt
> <craigmnet@REMOVEcow.physics.wisc.edu> wrote:
>
> <snip>
>> CURVEFIT - poor man's non-linear least squares original to IDL, based
>> on gradient expansion and not really robust.
> <snip>
>
> I always thought CURVEFIT was using Levenberg-Marquardt. Check the use
> of lambda, which allows the alternation between gradient and expansion
> method (which is the Levenberg-Marquardt as far as I know).

Regardless, CURVEFIT is nowhere near as robust as Craig's replacement for it. A while back
I used CURVEFIT on some data I was trying to fit (infrared sea surface emissivity that
depended on frequency, wind speed, and view angle) and, when I did get convergence, it
took forever. Using MPFIT (not changing anything else related to the data I was fitting),
I *always* got convergence and it ran orders of magnitude faster.

Single data point anecdotal evidence I know, but there you go.

cheers,

paulv

--
Paul van Delst Ride lots.
CIMSS @ NOAA/NCEP/EMC Eddy Merckx

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[Message index]

		Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? By: Paul Van Delst[1] on Thu, 08 March 2007 07:53
		Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? By: Wox on Thu, 08 March 2007 01:53
		Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? By: Craig Markwardt on Wed, 07 March 2007 18:07
		Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? By: duxiyu@gmail.com on Wed, 07 March 2007 17:19
		Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? By: duxiyu@gmail.com on Wed, 07 March 2007 17:08
		Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? By: news.qwest.net on Wed, 07 March 2007 07:02
		Re: What is the difference between 'curvefit', 'lmfit' and 'svdfit' procudure? By: Craig Markwardt on Wed, 07 March 2007 06:20

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