# multiplicative user-defined models

From: <rgibson_at_email.domain.hidden>
Date: Mon, 06 Nov 2006 14:28:08 -0500
Let's say I'm defining my own reddening fit model, similar to redden().  I use
add_slang_function() to register it with ISIS.  Call it myRedden().

Should myRedden return bin-integrated values (integrated over \Delta\lambda, the
bin width in Angstroms)?

If I use a fit_fun("myRedden(1) * powerlaw(1)"), powerlaw(1) is already
bin-integrated, so integrating myRedden would mistakenly throw in a factor of
bin-width, and it appears that ISIS does not account for that.  I.e., ISIS
assumes that only one component of a multiplicative model (term) is
bin-integrated.

Also, comparison with the get_model_counts() values returned by redden()
indicates that bin-integration would be wrong.

Do I understand this correctly?  If so, there is obviously potential for
confusion, especially if I use non-physical models like "poly(1) *
powerlaw(1)".  Just educating myself.

Thanks,
Rob
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Received on Mon Nov 06 2006 - 14:35:13 EST

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