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MPMINSTEP in mpfit? [message #94068]

Thu, 12 January 2017 23:08

Maryam
Messages: 16
Registered: July 2012

Junior Member

Hello.

I was wondering if we can specify the minimum change to be made in the parameter value in mpfit (i.e. similar to MPMAXSTEP but for min step)? The keyword .step specifies the minimum step size in the calculation of the derivatives but that's not what I want. I want to be able to tell mpfit what the minimum change in the parameters should be from one iteration to the next and let it figure out what step size to use for the calculation of the derivatives based on that. I noticed that earlier versions of mpfit.pro apparently had a MPMINSTEP but it seems to have been removed.

Any help is appreciated.
Maryam

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Re: MPMINSTEP in mpfit? [message #94073 is a reply to message #94068]

Fri, 13 January 2017 07:15

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Friday, January 13, 2017 at 2:08:12 AM UTC-5, Maryam wrote:
> Hello.
>
> I was wondering if we can specify the minimum change to be made in the parameter value in mpfit (i.e. similar to MPMAXSTEP but for min step)? The keyword .step specifies the minimum step size in the calculation of the derivatives but that's not what I want. I want to be able to tell mpfit what the minimum change in the parameters should be from one iteration to the next and let it figure out what step size to use for the calculation of the derivatives based on that. I noticed that earlier versions of mpfit.pro apparently had a MPMINSTEP but it seems to have been removed.

The short answer is, probably not.

If your concern is about how derivatives are calculated, use STEP. That will set a minimum size for the finite difference derivative step size.

If your concern is about parameter step size from one iteration to the next, then no, you can't set that. I experimented with it early on, but it never functioned properly.

Craig

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Re: MPMINSTEP in mpfit? [message #94079 is a reply to message #94073]

Fri, 13 January 2017 11:39

Maryam
Messages: 16
Registered: July 2012

Junior Member

Thank you!

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