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Re: Piecewise curve fitting in idl [message #61785 is a reply to message #61784]

Thu, 31 July 2008 07:00

d.poreh
Messages: 406
Registered: October 2007

Senior Member

On 31 Jul., 05:39, James Kuyper <jameskuy...@verizon.net> wrote:
> d.po...@gmail.com wrote:
>> On Jul 31, 1:21 pm, Wox <nom...@hotmail.com> wrote:
>>> On Thu, 31 Jul 2008 03:30:22 -0700 (PDT), d.po...@gmail.com wrote:
>>>> Folks
>>>> How we can do the piecewise curve fitting in idl. Say we have an array
>>>> that this array has got 2 or 3 trends in data and we want to fit a
>>>> liner curve for each trends. In MATLAB curve fitting tool, we can
>>>> easily exclude or include a part of data and then fit a curve. How we
>>>> can do this in IDL
>>>> Cheers
>>>> Dave
>>> Euhm, just do the fitting on the different parts? Or do you mean
>>> fitting with a piecewise polynomial (i.e. spline: see e.g. IMSL_BSLSQ
>>> or IMSL_CONLSQ)
>
>> just doing the fitting on the difrent part. how we can select this
>> parts and how we can fit a curve to these parts separatly?
>> Cheers
>
> Identifying the different parts is up to you. How do you know that there
> are 2-3 different trends? Whatever method you use to reach that
> conclusion will have to be adequate to identify where the different
> trends start and end. However, once you have identified the different
> parts you want fit separately, fitting each one separately is trivial:
> pass x[trend_start[i]:trend_end[i]] and y[trend_start[i]:trend_end[i]]
> to the curve-fitting routine.
>
> If you want a curve fitting routine that automatically figures out where
> each trend starts and ends, then it gets a LOT more complicated. You
> could do that by using a non-linear curve fitting routine, and make the
> transition point between the two trends be one of the parameters of your
> fitting curve. However, I would strongly recommend trying to understand
> why you see 2 or 3 different trends, and then try to come up with a
> single mathematical model for the entire curve that reflects that
> reason. Then fit that model to your data.- Zitierten Text ausblenden -
>
> - Zitierten Text anzeigen -

how we can do this in Iplot?

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[Message index]

		Re: Piecewise curve fitting in idl By: Wox on Fri, 01 August 2008 01:27
		Re: Piecewise curve fitting in idl By: jameskuyper on Thu, 31 July 2008 07:58
		Re: Piecewise curve fitting in idl By: pgrigis on Thu, 31 July 2008 07:41
		Re: Piecewise curve fitting in idl By: Paul Van Delst[1] on Thu, 31 July 2008 07:31
		Re: Piecewise curve fitting in idl By: David Fanning on Thu, 31 July 2008 07:03
		Re: Piecewise curve fitting in idl By: d.poreh on Thu, 31 July 2008 07:00
		Re: Piecewise curve fitting in idl By: jameskuyper on Thu, 31 July 2008 05:39
		Re: Piecewise curve fitting in idl By: d.poreh on Thu, 31 July 2008 04:54
		Re: Piecewise curve fitting in idl By: Wox on Thu, 31 July 2008 04:21
		Re: Piecewise curve fitting in idl By: Craig Markwardt on Sun, 03 August 2008 21:58

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