(unknown charset) Re: ISIS: loading data with proper statistical error

    
    Nicolas> When I load a spectrum using 
    Nicolas> id = data_load ("filename.pha");

via load_data(), I presume?

    Nicolas> it seems that the statistical errors are not calculated.

Is there a populated error column in the file?  You can use ftools, ciao
dmtools, or in isis:

  t = fits_read_table( "filename.pha" );
  print( t );

to check the file's content.

    Nicolas> I noticed that when I was trying to plot the data, but also when I do:

Depending on how you plot, you might not see the errorbars.

    Nicolas> data = get_data_counts(id);
    Nicolas> print (data.err);

Are they all 0.000?  You can use the low-level plotting to look at
arbitrary x,y values:

  plot( data.bin_lo, data.err );

or use various math functions:

  print( moment( data.err ) );


Some of the  spectral plotting functions don't plot error-bars by default:

  plot_data_counts( id );

doesn't, but

  rplot_counts( id ); 

does.  

To turn on errorbars, use

  errorbars( 1 );
  plot_data_counts( id );


Also see the help for errorbars:

 help errorbars


    Nicolas> Am I missing something?

    Nicolas> A solution could be to calculate myself this statistical
    Nicolas> uncertainty, e.g. doing: data.err = sqrt(data.value);

    Nicolas> but then, how to load this array back in the the dataset
    Nicolas> described by id??

See 

  help put_data_counts

or

  help define_counts

and

 help Minimum_Stat_Err

for detailed info.


(but you might just need to enable the histogram error plotting via errorbars())



-- Dave

David Huenemoerder  617-253-4283 (o); -253-8084 (f); http://space.mit.edu/home/dph
MIT Kavli Institute for Astrophysics and Space Research
One Hampshire Street, Room NE80-6065
Cambridge, MA  02139
[Admin. Asst.: Elaine Tirrell, 617-253-7480, egt_at_email.domain.hidden
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