Re: ISIS Equivalent Width Function

On May 4, 2007, at 3:51 PM, juan luna wrote:

> Thanks for the function and help. I have one more
> question about the EW:
>
> -I'm getting different values using Sherpa and ISIS.
> In Sherpa my data are HEG+-1 using add_grating_orders.
> In ISIS I'm using HEG+-1 and MEG+-1, and

I haven't done extensive tests against old Sherpa, and I don't know how 
it stacks up.  In general, however, barring me making a programming 
error in the S-lang code, I would be wary of Sherpa.  It wouldn't be 
the first bug we found there.

In as much as I've tested it head-to-head, my code seems to agree with 
the XSPEC definition of equivalent width.

> match_dataset_grids([3,1,2]);
> variable g = combine_datasets([1:4]);
>
> where 1 and 2 are HEG+-1 and 3,4 are MEG+-1.
>
> -I'm using a model like:
> fit_fun("powerlaw(1)+gaussian(1)+gaussian(2)+gaussian(3)");
>
> Using your EW function, I'm doing :
>
> eqw=eqw(g,3) for the gaussian(1).

And technically speaking, that is comparing to dataset 1, the HEG 
dataset.  I *don't* have this code set-up to use the combined data sets 
per se.  However, I don't think that should make any difference.

Also, note in the above that it should be:

	(eqw_ma, eqw_ev) = eqw(1,3)

Since I'm having it output in both eV and mA.

> -The EW that Sherpa is calculating are ~2 times the
> ones from ISIS. Any help with this?

I'd have to go and look at Sherpa again to see what's going on there.  
If I get a chance to run a test case, I'll let you know.

Cheers,

Mike


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