I have a very cumbersome expression, which I need to export to TeX form. The equations ends up to be extremely long, so I prefer that mathematica can display $\rm{Sin}[\alpha_1]$ as $s_{\alpha_1}$ , etc., and $\rm{Sin}[\alpha_1+\alpha_2]$ by $s_{\alpha_1+\alpha_2}$. Preferably, this notation will not prevent the expression from further trigonometric simplification.
I can't find a way after a lot of search. Could someone help?
Update
Thanks for the answers. They both work and have solved my problem, but I notice that they can no longer be further trigonometric simplified; for example,
Simplify[
Sin[Subscript[α, 1]]^2 /. Sin[x_] :> Subscript[s, x] + Cos[Subscript[α, 1]]^2]
does not simplify to 1. I wonder if there is anyway that avoid this problem? If this is possible, then the outputs within Mathematica itself can be more compact, and can be used for further manipulation, which is helpful.
MakeBoxes[Sin[x_], StandardForm] := MakeBoxes[Subscript["s",x], StandardForm]
and something similar for Cos[x], although you might want to create a function to only produce the compact output when needed. $\endgroup$