Re: ISIS: loading data with proper statistical error

On Thu, Nov 29, 2012 at 15:11 -0800, Nicolas Barrière wrote:
> Dear ISIS users,
> 
> I just started to use ISIS one week ago, and although I've been
> steadily becoming more comfortable with its use, I'm now stuck
> on a problem that should be very simple.
> 
> When I load a spectrum using 
> id = data_load ("filename.pha");

data_load is not an isis function -- I assume you mean 'load_data'.  

>
> it seems that the statistical errors are not calculated.
>
> I noticed that when I was trying to plot the data, but also when I do:
> 
> data = get_data_counts(id);
> print (data.err);
> 
> 
> Am I missing something?

Isis normally loads the STAT_ERR column from the PHA file and
verifies that the values are consistent with poisson
uncertainties (or with the value of Minimum_Stat_Err, if
Minimum_Stat_Err>0).

What columns appear in your PHA file?
Is Minimum_Stat_Err> 0?

> 
> A solution could be to calculate myself this statistical
> uncertainty, e.g. doing: data.err = sqrt(data.value);
> 
> but then, how to load this array back in the the dataset described by id??

It should not be necessary for you to do that, but if you want
to modify the statistical uncertainties, you can use
put_data_counts.

Thanks,
-John
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