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I'm using both the siunitx and isomath packages. I'm not sure whether there's a clash between those packages when it comes to Greek symbols in units. Indeed, isomath italicize capital Greek symbols (as it should to stay ISO-80000-2 compliant), while units should be upright. Therefore the ohm symbol Omega appears italicized when using \si{\ohm} while it should be upright; am I wrong? If not, how could I fix this issue? I.e. I'd like Omega to appear italicized when it's not used via siunitx, but I want it to be upright when using siunitx.

Edit: By creating a minimal example I realized that it isn't a clash between isomath and siunitx but cmbright and siunitx (I think!). Here's the example:

\documentclass[a4paper, 11pt]{article}
\usepackage{amsmath}
\renewcommand{\familydefault}{\sfdefault} % Sans serif font type.
\usepackage[margin = 2.6cm]{geometry}
\usepackage{siunitx}
\usepackage{isomath}
\usepackage{cmbright}

%%% fonts
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern} 
%%%

\begin{document}

Here I expect an upright Greek letter: \si{\ohm}. However it is italicized.

Here I expect an italicized Greek letter: $\Omega$. Right now, it works fine.

\end{document}

If I remove the line invoking cmbright, I get the behavior that I expect. But I do need that package. I use it so that the math fonts are sans serif and similar to my text fonts.

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    Welcome to TeX.SX! Please help us help you and add a minimal working example (MWE) that illustrates your problem. Reproducing the problem and finding out what the issue is will be much easier when we see compilable code, starting with \documentclass{...} and ending with \end{document}. – dexteritas Jul 25 '17 at 18:36
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    You have to provide a suitable definition for the symbol here: it's not possible to guess every possible font combination. – Joseph Wright Jul 25 '17 at 18:51
  • @dexteritas, I have edited my question to include a MWE. Maybe it needs further edits to display an image and also to modify the title since apparently the culprit isn't isomath but cmbright. – thermomagnetic condensed boson Jul 25 '17 at 19:10
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Load isomath after cmbright. Sometimes, package loading order makes a difference, especially when fonts are involved.

\documentclass[a4paper, 11pt]{article}
\usepackage{amsmath}
\renewcommand{\familydefault}{\sfdefault} % Sans serif font type.
\usepackage[margin = 2.6cm]{geometry}
\usepackage{siunitx}
\usepackage{cmbright}
\usepackage{isomath}

%%% fonts
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern} 
%%%

\begin{document}

Here I expect an upright Greek letter: \si{\ohm}. However it is italicized.

Here I expect an italicized Greek letter: $\Omega$. Right now, it works fine.

\end{document}

enter image description here

As I commented , however, the cmbright seems to be wiped out by the later loading of lmodern. One might, thus, have meant it this way. In either case, though, the isomath should be loaded later than cmbright.

\documentclass[a4paper, 11pt]{article}
%%% fonts
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern} 
%%%
\usepackage{amsmath}
\renewcommand{\familydefault}{\sfdefault} % Sans serif font type.
\usepackage[margin = 2.6cm]{geometry}
\usepackage{siunitx}
\usepackage{cmbright}
\usepackage{isomath}


\begin{document}

Here I expect an upright Greek letter: \si{\ohm}. However it is italicized.

Here I expect an italicized Greek letter: $\Omega$. Right now, it works fine.


\end{document}

enter image description here

  • That indeed fixed the problem, thank you very much! I'd appreciate a very brief explanation of why this work. I'm guessing it has to do with cmbright undoing things isomath does? – thermomagnetic condensed boson Jul 25 '17 at 19:15
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    @no_choice99 I'm guessing it has to do with cmbright undoing things isomath does? Without knowing the specifics, the answer is "yes." In general, one would want to define the math font families (in this case cmbright) before redefining how those fonts behave in various math circumstances (which is what isomath does). – Steven B. Segletes Jul 25 '17 at 19:21
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    @no_choice99 Of course, it would seem that lmodern clobbers the cmbright stuff, so I am not sure where exactly you want the answer to go... – Steven B. Segletes Jul 25 '17 at 19:26
  • Thanks again for your comment and edit in the answer. I'm confused on which fonts looks better now in your 2 displays of the fixed problem. In other words I'm confused on whether to load lmodern before the other 2 packages or if I should load it last. – thermomagnetic condensed boson Jul 25 '17 at 19:36
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    @no_choice99 My point is only that loading lmodern last would seem to eliminate altogether any effect of loading cmbright, since lmodern defines its own set of sffamily fonts. – Steven B. Segletes Jul 25 '17 at 19:39

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