Re: using warmabs model in ISIS

On Jun 6, 2013, at 3:34 AM, "Oliwia Madej" <O.Madej_at_email.domain.hidden
> 
> Has any of you used warmabs model before in ISIS ? If so perhaps you encountered a problem which I'm having 
> at the moment. After setting up all the variables necessary (warmabs_data, warmabs_pop) I load the model, try to fit it but the final values of the 
> parameters in the model (e.g. nh,xi,vturb) don't seem to change with respect to the initial values I put in 
> (which are already somewhat close to the good fit but not there yet). The parameters I mention are free of course during the fit. 
> I'm more familiar with xspec and the same warmabs model is working without problems there.

What Moritz said, probably.

The default fit method in XSPEC and ISIS are the same – essentially lmdif/mpfit – but the XSPEC version defaults to things like smaller fractional step sizes.  One thing that was noticed a few years back was that sometimes ISIS had trouble fitting lines to HETG data since the fractional step size on a parameter was larger than the HETG resolution.

In ISIS, the mpfit method is the same as the lmdif method, except that mpfit has tighter tolerances.  I usually default to lmdif, except when fitting lines to gratings data, in which case mpfit is my default.

But as Moritz says, you can change default parameters for any of the fit parameters.

That being said, please tell me that this isn't warmabs run on a Mac.  I haven't successfully gotten it to build on a Mac.  There's definitely some issues with the code that really become apparent when running it under ISIS on a Mac.

-Mike



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