This is correct. I assure you that the physics texts all tend to use i and j as index variables. Particularly for matrices, whose terms have a tendency to be wr

This is correct. I assure you that the physics texts all tend to use i and j as index variables. Particularly for matrices, whose terms have a tendency to be written as M_i_j. [1] Remember that modern electronic computing was invented by mathematicians and physicists. --- [1] HN isn't about TeX, so read that as "M sub-i sub-j".