Customizable latex for functions

[SimonKing]

There should be a way to customize how a function is printed and how it is translated into Latex, as requested on ​ask-sage.

I suggest, as a first step, to add methods set_name() and set_latex_name() that change the value of the cdefined attributes _name used for printing and _latex_name used for translation to latex. Then, the following would work:

sage: tan.set_name('tg')
sage: tan
tg
sage: tan.set_latex_name(r'\tg')
sage: latex(tan)
\tg

However, that can really only be the first step. Because, when I did so, I still got

sage: tan(x)
tan(x)
sage: latex(tan(x))
\tan\left(x\right)

Hence, in addition to that, the given latex name should be propagated to expressions.

[kcrisman]

Please upload that preliminary patch so others can work with it!

The SR stuff does come from Ginac, as I thought I remembered. Maybe Burcin will have a brief comment to put us on the right track for that; I don't quite understand how it works, though I think I once nearly figured it out :)

[SimonKing]

Preliminary patch: Change latex/repr of a function. But the custom names are not propagated.

[SimonKing]

Patch's up.

With it, this works

sage: tan.set_latex_name(r'\tg')
sage: latex(tan)
\tg
sage: tan.set_name('tg')
sage: tan
tg

but this doesn't

sage: tan(x)
tan(x)
sage: latex(tan(x))
\tan\left(x\right)

[kcrisman]

For reference for anyone implementing this correctly, in ​this thread on sage-support, Burcin recommends

It needs to go through the 
registry of functions stored in Pynac and update the name or the 
printing functions there.

[rws]

See also #20888