def gcPath(basePath,snapNum,chunkNum=0):
    """ Return absolute path to a group catalog HDF5 file (modify as needed). """
    gcPath = basePath + '/groups_' + str(snapNum).zfill(3) + '/'
    filePath = gcPath + 'groups_' + str(snapNum).zfill(3)
    filePath += '.' + str(chunkNum) + '.hdf5'
    
    return filePath