The published paper about the GRAPE package is:
L.H. Soicher, GRAPE: a system for computing with graphs and groups, in
"Groups and Computation" (L. Finkelstein and W.M. Kantor, eds.), DIMACS
Series in Discrete Mathematics and Theoretical Computer Science 11,
American Mathematical Society, 1993, pp. 287-291.
However, this reference describes GRAPE before it became an official
GAP share library package, and the best documentation on GRAPE is now
the chapter "Grape" in the GAP manual. This chapter is available online
in GAP in the usual way.
If you use GAP/GRAPE to solve a problem, then the above paper should
be referenced, as well as the GAP manual.
Regards, Leonard Soicher.