I've never heard of the matrix, but there is a popular technique called 21's.
For curls, (i use a cable) Its 7 bottom end curls, 7 full ROM curls and 7 top end curls. (i think in that order)...
Anyway, i have used that technique as a finisher or a final set on several exercises besides biceps.
be creative. This technique would best be utilized within a hypertrophy based program/week/day whatever.
Just another technique for your bag.