How can I show S-comma in LaTeX math mode?

Question

I am writing my bachelor's thesis and it needs to be written in Romanian. While writing some math formula, I wanted to write "and". It translates to "și". As it turns out, my LaXeTeX compiler can't render the ș (S-comma).

This is my code:

\begin{align}
       & \mathlarger{Fie\quad X(N) = x_0, x_1, x_2, \dots, x_{N-1}} \\
       & \mathlarger{unde\ N \in \mathbb{N} \ și\ k \in \{0,1,2,\dots,N/2\}} \\
       & \mathlarger{Avem:}
\end{align}

and this is the output:

How might I be able to show that S-comma?

Answer 1

Words, even without accents should not be in math italic, so

\text{unde} and \text{și}

Answer 2

In addition to rendering text-type words that may appear in a math expression in text mode (via a \text directive, say), you may want to execute a single \large instruction before entering math mode instead of executing \mathlarger at the start of every singe row in the align environment.

\documentclass{article} % or some other suitable document class
\usepackage[romanian]{babel}  % optional
%\usepackage{relsize} % for \mathlarger macro, not needed below
\usepackage{amsmath}  % for \text macro and align env.
\usepackage{amssymb}  % for \mathbb macro
\counterwithin{equation}{section} % just for this example
\begin{document}
\setcounter{section}{3}           % just for this example
\par 
\begingroup
\large % <-- execute this before entering display math mode
\begin{align}
       & \text{Fie}\quad X(N) = x_0, x_1, x_2, \dots, x_{N-1} \
       & \text{unde $N \in \mathbb{N}$ și $k \in {0,1,2,\dots,N/2}$} \
       & \text{Avem:}
\end{align}
\endgroup
\end{document}

Answer 3

If you really want larger font size in the display, you can avoid \mathlarger, but I'd not do it: a math display is already prominent enough.

In any case, you need \text for textual parts in math material.

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{etoolbox}
\usepackage{lipsum}
\makeatletter
% see https://tex.stackexchange.com/a/288889/4427
% detach \eqref processing from \tag processing
\let\tagform@ref\tagform@
\let\maketag@@@ref\maketag@@@
\patchcmd{\eqref}{\tagform@}{\tagform@ref}{}{}
\patchcmd{\tagform@ref}{\maketag@@@}{\maketag@@@ref}{}{}
% redefine \tagform@ to use the current size
\def\tagform@#1{%
  \maketag@@@{\saved@size(\ignorespaces#1\unskip@@italiccorr)}%
}
% in general \saved@size does nothing
\def\saved@size{}
% now we define a wrapper
\NewDocumentEnvironment{largerdisplay}{O{\large}mb}
 {% #1 = desired size (default \large), #2 = type of display, #3 = body
  \protected@edef\saved@size{\fontsize{\f@size}{0}\selectfont}%
  $$\begin{minipage}{\displaywidth}
  \abovedisplayskip=0.8ex \belowdisplayskip=\z@
  #1\noindent
  \begin{#2}#3\end{#2}%
  \end{minipage}$$}{\ignorespacesafterend}
\makeatother
\begin{document}
\lipsum[1][1-4]
\begin{largerdisplay}{align}
  & \text{Fie } X(N) = x_0, x_1, x_2, \dots, x_{N-1} \
  & \text{unde }N \in \mathbb{N} \text{ și } k \in {0,1,2,\dots,N/2} \
  & \text{Avem:}
\end{largerdisplay}
\lipsum[2][1-4]
\end{document}

Compare with the simple align: