How can I create index for a word in legend?

Hi When I wrote legend(' Gamma_xz') only x goes to index. However I want that both xz goes to index of the word Gamma.

In other word, in legend, if I want to write (x sub i)I could write (x_i) then 'i' will go to index but if my index has more than one character like (x sub ij), than only the first charter will appear as index . I would be appreciated if you guide me how can I fix it.

Answer 1

[Azzi Abdelmalek]

legend(' Gamma_x_z')