comparisonmath-moderomantext-mode
What is the difference between \text, \textrm, \textnormal, and \mbox (and possibly other commands commonly used to produce text in math mode)?
Various (La)TeX tutorials teach different methods, and I am sure that there is either a best one or there are subtly different usage scenarios.
I guess what you are seeing is the following when you use \mathrm with a serif font:
\documentclass{beamer}
\usepackage{amsmath}
\begin{document}
\begin{frame}
\( x y \mathrm{x} \text{\textup{x}}\)
\end{frame}
\end{document}
There are two ways to fix this: one fairly drastic option is to put
\renewcommand{\rmdefault}{cmss}
but this may feed through to places you are not expecting. An alternative is to replace the two relevant definitions from beamerbasefont.sty by
\AtBeginDocument{%
\SetMathAlphabet{\mathrm}{normal}{\encodingdefault}{cmss}{\mddefault}{n}
\SetMathAlphabet{\mathrm}{bold}{\encodingdefault}{cmss}{\bfdefault}{n}}
in your preamble. In the beamer style file {cmss} is {\rmdefault}.
Applied to the above example, either method gives you:
I'm afraid you hit no correct choice. ;-)
$\fT_\text{triv} = \Set{\emptyset, X}$: incorrect. Define
\newcommand{\ts}[1]{\textnormal{#1}} % textual subscript
and use $\fT_{\ts{triv}}. You can later change your mind about the typesetting of \ts. With \text you're not guaranteed to get upright shape, for example in the statement of a theorem.
$g \circ f = \text{id}_X$: incorrect. Define
\newcommand{\id}{\textnormal{id}}
(or with \textit, which I'd prefer).
$\text{Isom}(X)$: incorrect. It's an operator, so $\operatorname{Isom}(X)$. Defining a command with \DeclareMathOperator is of course a good choice. The same considerations hold for “grad”, “cov”, ”sgn” and ”Gal”.
\[ \text{Let } x = \text{ number of cats} \]: incorrect. “Let” should not go in the displayed equation. So
Let
\[
x=\text{number of cats}
\]
with no space before “number”.
The longer one should be
\begin{align*}
U \subseteq \mathbb{R}^n \text{ offen} \Leftrightarrow
&\text{für jedes $x \in U$ gibt es $r > 0$,}\\
&\text{sodass $\fB_r(x) = \Set{y \in \mdr^n | d(x,y) < r} \subseteq U$}
\end{align*}
so you don't have to think where spaces are necessary.
I wouldn't use a macro \Set with delimited argument, preferring
\newcommand{\Set}[2]{\{\,#1\mid #2\,\}}
and \Set{y \in \mdr^n}{d(x,y) < r}. This is more consistent with LaTeX syntax. If your \Set macro has just one normal argument, then use \mid and not |.
Best Answer
Update: Example added without
amstextto show the effect of this package on the other\text...commands.Example file without package
amstext(oramsmath):Example file with package
amstext:\mboxuses the current text font. The size is constant and does not change in subscripts, superscripts, fractions, …\textof packageamstext(oramsmath) uses the current text font, but adapt the size according to the current math style. Therefore it needs\mathchoicethat has an efficiency impact that the text is set four times for all math styles and later, when TeX knows the math style, it chooses the right version.\textrmuses the text roman font, but the other font parameters like encoding, shape and series are taken from the current text font. Font size is only adapted to the current math style if packageamstext(oramsmath) is loaded.\textnormaluses\normalfont, the size is only adapted to the currrent math style if packageamstext(oramsmath) is loaded.\mathrmuses the math roman font that might differ from the text roman font. Also the spacing is done according to math and the encoding differs from the text encoding.For text in math I would load package
amstext(oramsmath) and use\textor\textnormal.\textis shorter to type, but the dependency on the current text font might be sometimes an advantage, sometimes a disadvantage. For subscripts I would prefer\textnormal:But additional text might be better set in the current text font: