Re: fitting multiple data sets with variable norm

Hi,

> On May 16, 2011, at 1:36 PM, Rob Gibson wrote:
>> didn't realize you could pass Isis_Active_Dataset like that.

Since I also didn't realize for quite some time which powerful things
one can do with Isis_Active_Dataset as a model identifier, I'd like to
add another example:

    fit_fun("constant( (Isis_Active_Dataset-1)/4 ) * ...");

Because of integer arithmetics, the quotient gives
   1  for index  5-- 8,
   2  for        9--12, and
   3  for       13--16,
i.e., does the same job as the following function (which I believe
somehow needs to be defined as public in the "isis" namespace):

Michael Nowak wrote:
> define cst()
> {
>    if( 5 <= Isis_Active_Dataset <=8 )
>    {
>        return constant(1);
>    }
>    else if( 9 <= Isis_Active_Dataset <=12 )
>    {
>        return constant(2);
>    }
>    else if( 13 <= Isis_Active_Dataset <=16 )
>    {
>        return constant(3);
>    }
>    else
>    {
>        return constant(3);
>    }
> }

There is no doubt that the code provided by our friend in Cambridge, MA
is the much cleaner one; my example is just meant to illustrate ISIS'
capabilities.

A merged approach could read:

    public define flux_level(id)
    {
       return 5<=id<=8 ? 1               % low  flux
                       : 9<=id<=12 ? 2   % med. flux
                                   : 3;  % high flux (or other spectra)
    }
    fit_fun("constant( flux_level(Isis_Active_Dataset) ) * ...");

Since Isis_Active_Dataset is a global variable, it would not even have
to be passed as an argument to the flux_level function, see Mike's
example. Another maybe useful hint is therefore, especially if the fit
function contains >>1 (e.g., 2) occurrences of Isis_Active_Dataset: :-)

    public define IAD()  { return Isis_Active_Dataset; }
    fit_fun("constant( flux_level(IAD) ) * ...");

> John has also built in infrastructure (whose syntax I'm forgetting  
> at the moment)
> to assign model expressions just to specific datasets that can achieve the
> same thing.

You probably think of the assign_model function.
But I have never used it either, fully agreeing with the statement:

> But it's nice to have the Isis_Active_Dataset with which to program.

Cheers,

Manfred

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