Upright matematical letters in every environment

Question

I apologize in advance if this question has already been asked, and if it is a dumb question: my knowledge of LaTeX is very limited.

I'm doing a thesis in mathematics, and I've some problems regarding formulas, which sometimes appear upright -like using \text{}-, sometimes in italic -like using \emph{}-.

I divided the claims in two groups: \theoremstyle{plain} -for theorems, propositions, etc- and \theoremstyle{definition} -for definitions, remarks-.

Now, I use many times the letter $\text{H}$ to denote the cohomology: I therefore defined a new command

\newcommand{\coh}{\emph{H}}

but unfortunately, when is used in a definition, it is in italic, while in a theorem environment it is straight: how can I impose to LaTeX to always print this letter upright, no matter the environment in which is used? I tried \newcommand{\coh}{\text{H}} but it still doesn't work.

Answer 1

You should use \DeclareMathOperator{\coh}{H} which yields the same results in normal usage and in italics:

Code:

\documentclass{article}
\usepackage{mathtools}
\DeclareMathOperator{\coh}{H}
\begin{document}
In normal usage we have an upright $\coh$.
In emphasized text it appears the same \emph{$\coh$}.
\end{document}

Answer 2

You can use \textnormal{H}, to reset the formatting. The \text command inherits the formatting the surrounding text. That is, because a theorem statement is italicized, the italics will bleed through into math formulas. So would bold or sans-serif or small-caps formatting if you use $\text{H}$ in a header.

You can instead use \mathrm{H}, which is always upright, and spaced like an ordinary math symbol. If you use \DeclareMathOperator, you will get spacing like log or sin.

The unicode-math package gives you the choice between \mathrm (which uses the text font, but can be changed) and \symup (which uses the math font, but can be changed). This allows you to use distinct fonts for ordinary words in math mode, and for upright math symbols. (You might try upright italics, or Neo Euler.)

If you want to inherit the weight but reset the shape (so that a formula in a bold header is bold), you can use \textup{H}. Alternatively, \text{\rmfamily\upshape H} lets you set font axes individually.

It would be a good idea to define commands like this once, in the preamble.