# How to automate x[i]→x_{i}?

I have several Mathematica expressions in which subscripts are expressed with square brackets. E.g. x[12] is meant to represent x12, etc. If I evaluate TeXForm on such an expression, x[12], e.g., gets converted to x(12). Is there a way to get it to produce the x_{12} form instead?

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The problem is then telling apart x[2] which is meant to be $x_2$ and f[x] or f[0] which are $f(x)$ or $f(0)$. –  Szabolcs Jan 12 '13 at 23:10

Probably the easiest solution here is to use

Format[x[arg_],TraditionalForm]:=Subscript[x, arg]


This makes sure that the subscript form is used when the display is in TraditionalForm, which is also an intermediate step in creating TeXForm. Then you get for example

1+x[13]//TeXForm


$x_{13}+1$

The Format can't be specified directly for TeXForm because then expressions where your x[12] is surrounded by other things as in 1 + x[12] won't get translated correctly.

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Your answer suggests that Mathematica itself can render TeX. Can it? –  kjo Jan 12 '13 at 22:29
To a certain extent you can render $\LaTeX$, but it's very incomplete. The general idea is to use something like TraditionalForm@ToExpression["\\sin\\alpha", TeXForm, HoldForm]. I discussed this in this answer –  Jens Jan 12 '13 at 22:50
I just realized you may be looking for something simpler: when we say "render" $\LaTeX$, it could also mean to produce traditional-looking formulas from Mathematica standard form input. That is simply done by wrapping any such input in TraditionalForm[ ...]. You could say TraditionalForm is Mathematica's "pretty-print formula" typesetting mode. –  Jens Jan 13 '13 at 0:12