NAME

    gtltsum - Adds together livetime cubes produced by gtltcube.

USAGE
    
    gtltsum infile1 infile2 outfile


DESCRIPTION

    This tool facilitates multi-epoch analyses by summing the livetime
    contributions from each of two or more user specific input files
    and merges their GTI extensions. It checks to ensure that the
    input data sets are based on compatible HEALPix projection before
    they are summed. HEALPix is an acronym for Hierarchical Equal Area
    isoLatitude Pixelization (http://healpix.jpl.nasa.gov/). This is
    the only consistency check that is made between files. The input
    livetime cube files could be generated by gtltcube (see the
    gtltcube help) or obtained from the FERMI Science Support Center
    (FSSC).


PARAMETERS

    infile1 [file] 
    This is the name of the first livetime cube file or an ASCII file
    containing a list of livetime cube files, prepended with an "@"
    sign.  The livetime cube file could be generated by gtltcube (see
    the gtltcube help) or be obtained from the FSSC.
     
    infile2 [file]
    This is the name of the second livetime cube file. It will be prompted
    for only if the first file is also a livetime cube file (i.e., not a
    list of files).
     
    (table = EXPOSURE) [string]
    Name of the extension containing the livetime. This is a hidden
    parameter. The default value is EXPOSURE.

    (table2 = WEIGHTED_EXPOSURE) [string]
    Name of extension containing livetime.
    
    outfile [file]
    Output FITS file name.
     
    (chatter = 2)    
    This parameter fixes the output verbosity: no screen output (0),
    nominal screen output (2), maximum verbosity (4). The default value is
    2.
    
    
    (clobber = yes) 
    If true, an existing file of the same name will be overwritten.
    
    (debug = no)
    Activate debugging mode. This is a hidden parameter. The default
    value is "no". When debug is "no", all exceptions that are not
    caught and handled by individual tool-specific code are caught by
    a top-level exception handler that displays information about the
    exception and then exits. When debug is "yes", such exceptions are
    not caught by the top level code. Instead the tool produces a
    segmentation violation, which is more useful for debugging. When
    debugging mode is enabled, the tool produces more verbose output
    describing any errors or exceptions that are encountered.
    
    (gui = no)
    Graphical user Interface (GUI) mode activated if "yes" is
    specified. This is a hidden parameter. The default value is "no".
    
    (mode = ql) 
    Mode of automatic parameters. This is a hidden parameter. The default
    value is "ql".

EXAMPLES

    Parameters are passed following the FTOOLs model. They could be passed
    answering from a prompt, as a list in a command line, or by editing
    the parameter file.
 
    To be prompted for gtltsum simply type in the command line: 

> gtltsum
 
    You will be prompted for parameter values. Beware that not all
    parameter are prompted; some of them are "hidden".  If you want to
    change one of the "hidden" parameter you should specify the values in
    the command line. For example if you do not want to overwrite an
    existing file you should type in the command line:
 
> gtltsum clobber=no
  
    An example of how to run the tool is given below: 

> gtltsum
Livetime cube 1 or list of files [] : expCube_000001.fits
Livetime cube 2 [none] : expCube_000002.fits
Output file [] : expCube.fits

    That last example could be also run in the command line as follows:

>gtltsum infile1=expCube_000001.fits infile2=expCube_000002.fits
 outfile= expCube.fits


KNOWN BUGS

SEE ALSO

     gtltcube
