Do you have a full license of Prime, or are you using Prime Express 4?
(In Express you cannot enter programs).
The function is a bit awkward. What is gmr ?
Who are x and y?
You can do it this way:
Call up the Matrix-index (Depends on the ORIGIN Variable which is in "calculations" defined)
The simplest way to enter x sub m is by typing:
x [ m
Unless you happen to have the German language version of Prime where (according to Volker's picture) you'd have to type:
x <Ctl-Alt-[> m
where <Ctl-Alt-[> is pressing down the Ctrl key and the Alt key simultaneously and while they are down you hit the [ key once. Seems
pretty much too cumbersome to me for such an often-used feature!