| Re: MPFIT2DPEAK with constraints [message #36636] |
Fri, 10 October 2003 07:51 |
c.carrano
Messages: 2
Registered: October 2003
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Junior Member |
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Craig Markwardt <craigmnet@REMOVEcow.physics.wisc.edu> wrote in message news:<onzng9lrud.fsf@cow.physics.wisc.edu>...
> c.carrano@att.net (Charles Carrano) writes:
>> Greetings. I'm trying to understand how Craig
>> Markwardt's peak fitting function MPFIT2DPEAK
>> works when you wish to require that certain
>> parameters be held constant.
>>
>> Specifically, I know that my data should peak
>> at the origin and so I'd like to force the
>> fitted Gaussian to peak there as well.
>>
>> Despite specifying that A[4] and A[5] be
>> fixed using the PARINFO structure, the fitted
>> Gaussian is not centered at the origin.
>> Supplying PARINFO to MPFIT2DPEAK does change
>> the fit but it actually makes it slighly worse.
>> Anyone know what I might be doing wrong?
>
> Greetings--
>
>> zfit = mpfit2dpeak(z, a1, x, y, /tilt, PARINFO=pi)
>
> The documented way to enter the initial parameters to MPFIT2DPEAK is
> using the ESTIMATES keyword.
>
> Craig
Thank you. I had inadvertently confused the functions
of the parinfo.value and ESTIMATES parameters. Passing
ESTIMATES=a0 to mpfit2dpeak fixes the sample code
above. Thank you for your help and, of course, your
valuable software contribution to the scientific
community.
- Charles
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| Re: MPFIT2DPEAK with constraints [message #36640 is a reply to message #36636] |
Thu, 09 October 2003 20:00  |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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c.carrano@att.net (Charles Carrano) writes:
> Greetings. I'm trying to understand how Craig
> Markwardt's peak fitting function MPFIT2DPEAK
> works when you wish to require that certain
> parameters be held constant.
>
> Specifically, I know that my data should peak
> at the origin and so I'd like to force the
> fitted Gaussian to peak there as well.
>
> Despite specifying that A[4] and A[5] be
> fixed using the PARINFO structure, the fitted
> Gaussian is not centered at the origin.
> Supplying PARINFO to MPFIT2DPEAK does change
> the fit but it actually makes it slighly worse.
> Anyone know what I might be doing wrong?
Greetings--
> zfit = mpfit2dpeak(z, a1, x, y, /tilt, PARINFO=pi)
The documented way to enter the initial parameters to MPFIT2DPEAK is
using the ESTIMATES keyword.
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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