How to right-align part of an equation in display math mode

Question

This is over a single line. I honestly thought it would be very simple but so far I have tried:

\hfill
\hspace*{\fill}
\null\hfill
\hspace*{0pt}\hfill
\mbox{}\hfill

In the following line:

$$g(x) = \underset{c \in \mathcal{Y}}{\operatorname{arg max}} \mathcal{P}(f(x + \epsilon)=c), \hfill \epsilon \sim \mathcal{N}(0, \sigma^2I)$$

All of them result in:

If I just use inline math-mode with a new line, it results in the main equation being left-aligned. I want the main equation to be centrally aligned, with the noise right-aligned.

@Someone flalign only works over multiple lines I believe? At least in this case using an ampersand doesn't move the noise to the right. — Somniare, Aug 20 '23 at 15:34
You seem to want something like \begin{equation} g(x)...c), \tag{\epsilon \sim ...} \end{equation}. I'm pretty sure this is a duplicate. — barbara beeton, Aug 20 '23 at 17:40
@barbarabeeton ah yes, that works, thank you! I couldn't find any the same question anywhere. — Somniare, Aug 20 '23 at 17:55
@Somniare -- Here's one: https://tex.stackexchange.com/q/420314 I used the search terms "tag flush right". — barbara beeton, Aug 20 '23 at 19:58

score 0 · Accepted Answer · answered Aug 20 '23 at 21:30

I'd use the last realization, as there is no reason for shoving the side condition to the right margin.

In any case, $$ should never be used in a LaTeX document environment. Also note \operatorname* instead of \underset.

\documentclass{article}
\usepackage{amsmath}
% these two packages just for the example
\usepackage{lipsum}
\usepackage{showframe}
\begin{document}
\lipsum[1][1-4]
[
\hspace{1000pt minus 1fill}
g(x) = \operatorname{arg,max}_{c \in \mathcal{Y}}\mathcal{P}(f(x + \epsilon)=c), 
\hspace{1000pt minus 1fill}
\epsilon \sim \mathcal{N}(0, \sigma^2I)
]
\lipsum[2][1-4]
[
\hspace{1000pt minus 1fill}
g(x) = \operatorname{arg,max}{c \in \mathcal{Y}}\mathcal{P}(f(x + \epsilon)=c), 
\hspace{1000pt minus 1fill}
\makebox[0pt][r]{$\displaystyle \epsilon \sim \mathcal{N}(0, \sigma^2I)$}
]
\lipsum[3][1-4]
[
g(x) = \operatorname*{arg,max}{c \in \mathcal{Y}}\mathcal{P}(f(x + \epsilon)=c), 
\qquad \epsilon \sim \mathcal{N}(0, \sigma^2I)
]
\lipsum[4][1-4]
\end{document}

How to right-align part of an equation in display math mode

1 Answers1