Re: Simultaneous fit

On Fri, Apr 18, 2003 at 15:38 -0400, Marc Audard wrote:
> Hi-
> 
> If I would like to fit simultaneously HEG-1 and HEG+1 but leave the 
> wavelength
> free and different in each detector (to account for calibration errors), how
> can I do this? Furthermore, will get_params save each parameter, so
> that I can use them later and so that fakeit will use wavelength 1 for 
> dataset 1
> and wavelength 2 for dataset 2?
> 
> Thanks
> 
> Marc


Hi Marc,

Shifting wavelengths is possible but I must admit that the
appended example code is mostly untested (apart from verifying
that it produces the plots that I expected).  I _think_ it does
what you want -- please let me know if it doesn't.

In the example, I defined a fit-operator which handles the grid
shift and which allows each dataset to have its own wavelength
shift. fakeit uses the current fit-function, so the wavelength
shifts come from the fit-function definition.

To answer your other question -- yes, get_params() will return
an array of structures containing information on all the
fit-parameters.  Within a script, those values can be restored
using set_params():

   variable p = get_params();

    ..... do stuff, maybe change the fit-parameters...

   set_params(p);  % restore the saved parameters.

Hope that helps,   

-John

-- 
John C. Houck                       MIT Center for Space Research
NE80-6005: 617-253-3849                   77 Massachusetts Avenue
42:21:55.105N, 71:05:28.122W             Cambridge, MA 02139-4307



% load 2 datasets for this example:

load_dataset ("o1318_heg+1_pha.fits",
	      "acisheg1D1999-07-22rmfN0003.fits.gz",
	      "acisf01318_000N001HEG_1_garf.fits.gz");
load_dataset ("o1318_heg-1_pha.fits",
	      "acisheg1D1999-07-22rmfN0003.fits.gz",
	      "acisf01318_000N001HEG_-1_garf.fits.gz");

% wlshift is an operator-function (somewhat like xspec's
% convolution models).  It wavelength-shifts the result of
% any model by an amount specific to each dataset.

define wlshift_fit (l,h,p,val)
{
   variable offset;

   switch (Isis_Active_Dataset)
     {
      % datasets 1 and 3 get shifted by "offset1" = p[0]     
      case 1 or case 3:
	offset = p[0];
     }
     {
      % datasets 2 and 4 get shifted by "offset2" = p[1]
      case 2 or case 4:
	offset = p[1];
     }
     {
	% default
	error("*** wlshift: unsupported dataset index");
	return -1;
     }

   return rebin (l, h, l+offset, h+offset, val);
}
add_slang_function ("wlshift", ["offset1", "offset2"]);
set_function_category ("wlshift", ISIS_FUN_OPERATOR);

% apply the wavelength shift to a delta-function line

fit_fun ("wlshift (delta(1),1)");

set_par ("delta(1).norm", 1.e-2);
set_par ("delta(1).lambda", 12);

set_par ("wlshift(1).offset1", -0.5);
set_par ("wlshift(1).offset2", +0.5);

list_par;

% evaluate the model to make sure the shifts are applied:

() = eval_counts;
plot_model_counts(1);
oplot_model_counts(2);

% now create 2 fake datasets

assign_rmf(1,3);
assign_arf(1,3);

assign_rmf(2,4);
assign_arf(2,4);

fakeit;

xrange(11,13);

plot_pause;
rplot_counts(3);

plot_pause;
rplot_counts(4);
----
You received this message because you are
subscribed to the isis-users list.
To unsubscribe, send a message to
isis-users-request_at_email.domain.hiddenwith the first line of the message as:
unsubscribe