simple_gpile2

Hi Maria-

I've taken the liberty of signing you up in the isis-users mail list, so you can 
post further questions and get replies.  (Not to worry - it's a low key group 
without tons of postings.)

The issue is that simple_gpile2 is a convolution model, which has the syntax:

	generic_model(#)*other_generic_model(#) + convolution_model ( #, other_model_expression )

Note the positioning of the model identifier # and the parantheses, with the
model expression to be convolved inside the convolution model
parantheses.

So, in the below, I would do:

	fit_fun("simple_gpile2(Isis_Active_Dataset, constant(Isis_Active_Dataset)*tbabs(1)*diskbb(1))");

(fit_fun being the ISIS command, "model" being the alias I also use for it 99.9% 
of the time, but  I just wanted to be clear on what's generic ISIS and what's from
scripts.)  I'm not sure what you're using the constant for (MEG/HEG crossnorm?),
but you likely want that part of the pileup modeling.

Note that convolution models are the only ones that have a special syntax in 
ISIS.  It otherwise makes no distinction between "additive" and "multiplicative"
models.  Models are just vectors of numbers, which you can use however
you want.  If they're a model from XSPEC, there's probably a way they were
meant to be used, but some like "constant" I have certainly used both
as additive and multiplicative.

To get hyper-technical with simple_gpile2, you would renormalize the HEG
and MEG ARFs, since we put some of the effective area into the RMFs, and
not the ARFs.  (I.e., gratings RMFs are not unit normalized.)  In the absence
of pileup, ARF*RMF = response works fine, but in simple_gpile2 we want all
the effective area in the ARFs.  

I've got this  described in the appendix of Nowak et al. 2008, ApJ 689, p. 1199. 
We put on order of 5% of the effective area into the RMFs, so assuming an 
~20% pileup correction, doing this change might be something like a 5%*20% 
~ 1% change to the total spectrum.

Anyhow, write back to isis-users if you need more help.

-Mike

Begin forwarded message:

> Dear ISIS experts,
> 
> I am trying to use the simple_gpile2 routine in ISIS to correct for 
> pile-up in my HETGS observations.
> I have loaded HEG1 and MEG1 spectra and fitted them with a simple model. 
> Then, I add
> simple_gpile2 to the model as follows:
> 
> model("constant(Isis_Active_Dataset)*simple_gpile2(Isis_Active_Dataset)*tbabs(1)*diskbb(1)");
> 
> Then, I thaw the parameter called beta for both datasets and try to make 
> a fit. However, I get the
> error below, which is really cryptic to me.
> 
> Could you please advise me or point me to some documentation on the use 
> of this routine? (I already
> checked the pileup ABC guide and Hanke 2009 paper, but I still don't 
> understand what may be causing
> the error).
> 
> Many thanks in advance,
> 
> Maria
> 
> Error: /Users/mdiaztri/SciSW/isis-1.6.2/src/fit-cmds.c:2328
> Error: /Users/mdiaztri/SciSW/isis-1.6.2/src/fit-cmds.c:2328
> Stack Underflow Error
> ***string***:1:__isis_tmp_ffname__:Stack Underflow Error
> Error encountered while executing __isis_tmp_ffname__
> Error :/Users/mdiaztri/SciSW/isis-1.6.2/src/fit-cmds.c:1869
> Failed: evaluating model
> Error :/Users/mdiaztri/SciSW/isis-1.6.2/src/fit-cmds.c:1869
> Failed: evaluating model
> Traceback: _fit
> /Users/mdiaztri/SciSW/isis/1.6.2/share/fit-cmds.sl:1176:_do_eval_fit:Stack 
> Underflow Error
>   Local variables for _do_eval_fit:
>     Ref_Type _do_eval = &_isis->_fit
>     Integer_Type data_type = 0
>     String_Type msg = "s = fit_counts ([&info_struct])"
>     Integer_Type nargs = 0
>     Struct_Type tmp = Struct_Type with 4 fields
>     Ref_Type ref = Local variable reference
>     Integer_Type response_type = 0
>     Integer_Type saved_fit_verbose = 0
>     Null_Type fit_verbose = NULL
>     Undefined_Type status = Undefined_Type
> /Users/mdiaztri/SciSW/isis/1.6.2/share/fit-cmds.sl:1191:fit_counts:Stack 
> Underflow Error
>   Local variables for fit_counts:
>     String_Type msg = "s = fit_counts ([&info_struct])"
> <stdin>:42:<top-level>:Stack Underflow Error


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