When an application prompts the user for a catalogue or NDF using the facilities of the CAT (see SUN/181) or NDF (see SUN/33) libraries, the user may only reply with the name of a single catalogue or NDF respectively. If the user has many files to process in the same fashion, it can prove tedious to repeat the commands for each input dataset. Now one solution is to write a script that loops, executing the various applications for each input file. More elegant and convenient to users would be to allow a group of files to be processed in a single command. This is what LPG offers. The group or list is supplied to the relevant ADAM parameter, possibly defined using wildcards. Using LPG enhances your application package to users.
Note the rôle of LPG is different from NDG or CTG libraries. While these supply groups of NDFs and catalogues, again with wildcards (via the underlying GRP library) these are processed in the same invocation of an application. Examples of this method include forming a flat field from a series of CCD image NDFs, and merging catalogues.