Invalid LaTeX format for arcsec2

astropy version 3.1.2

print (astropy.units.Unit("arcsec2").to_string("latex")) $\mathrm{{}^{\prime\prime}^{2}}$

This is invalid LaTeX because the same base string carries two exponents. The problem arises because the LaTeX string for arcsec uses an exponent to raise the primes above the baseline.

A quick fix would be to always enclose the LaTeX string for arcsec in curly braces, but the resulting layout is not so nice (the primes and the exponent are on the same level). The better fix would be to include the LaTeX string for arcsec in regular parentheses if and only if it carries an exponent.

[mhvk]

Hmm, I think with an exponent we should indeed not use the primes at all, but rather just $\mathrm{arcsec}^{2}$. Arguably this should happen in composite units as well (say, pix/arcsec). A change is not entirely trivial - the actual formatting is done in Latex.to_string in units/format/latex.py.

Note that there is already a special treatment for arcsec in si.py, in that only the un-prefixed unit is shown using primes. The same should also be done for arcmin and deg. Right now:

In [12]: u.mdeg.to_string('latex')
Out[12]: '$\\mathrm{m{}^{\\circ}}$'

(And the same for unicode output)

Possibly the simplest would be for the format dict to def_unit to include an extra latex_simple (or so) entry with the value that gets used when the unit is shown on its own.

[mhvk]

fixed by #9218