Basic: How can I stop centering a text?

Question

I'm starting with LaTeX and have a basic question regarding formatting of paragraphs. I wanted to caption an equation mid text, but I couldn't find any convenient way without the equation floating away, so I decided to center a line in the next paragraph as a sort of caption. For that, I had to center the text using \centering. How can I prevent the following paragraphs from being centered and instead being "normal"?

Answer 1

1. Note that the approach of {\centering Text} of the accepted answer will not work because there are not a blank line (=\par) before of the closing brace. The same apply to \begingroup\centering ... \endgroup

2. Note also that the center environment add a noticeable vertical spacing before and after the caption (that could be or not what you want).

3. For one line caption without additional space is enough a \hfil after the equation.

4. If you left a blank line between a display math mode and \hfil, be aware that the text is centered taking into account the paragraph indentation.

5. Alternatively to \hfil you can use also a \makebox wide as to the line width, since its content is centered by default. Unnecessarily complicated to obtain the same, unless you want a wide \fbox around the caption or so.

MWE (blank lines are converted to \par to remark where they are.):

\documentclass{article}
\begin{document}
\[ a^2+b^2=c^2 \]
\hfil This is the Pythagorean Theorem.\par           % works 
\hfil This is the Pythagorean Theorem.\par           % works if \parindent is 0pt
\begin{center}
This is the Pythagorean Theorem.                     % note the vertical spacing 
\end{center}
{\centering This is the Pythagorean Theorem.}\par    % oooooopps !
{\centering This is the Pythagorean Theorem.\par }   % works
\noindent\makebox[\textwidth]{This is the Pythagorean Theorem.}\par % works too
\end{document}

Edit:

By the way, to use formula with captions I will make a new type of float or true captions without floats, MWE:

\documentclass{article}
\usepackage{amsmath,lipsum}
\usepackage{float}
\floatstyle{boxed}
\floatname{eq}{Equation}
\newfloat{eq}{H}{eqn}
\usepackage{caption}
\captionsetup[eq]{skip=20pt,position=top}
\begin{document}
\lipsum[2]

\begin{eq}
\[ a^2+b^2=c^2 \]
\caption{This is the Pythagorean Theorem.}
\end{eq}

\begin{eq}
\[\mathbf{F} = \frac{d \mathbf{p}}{dt} = \frac{d (m \mathbf{v})}{dt} =  m \frac{d \mathbf{v}}{dt} = m\mathbf{a}\]
\caption{Newton's second law of motion}
\end{eq}

\lipsum*[13] Or maybe mora compact and simple fake floats: 

\[ a^2+b^2=c^2 \] 
\captionof{eq}{This is the Pythagorean Theorem.}

\[\mathbf{F} = \frac{d \mathbf{p}}{dt} = \frac{d (m \mathbf{v})}{dt} =  m \frac{d \mathbf{v}}{dt} = m\mathbf{a}\]
\captionof{eq}{Newton's second law of motion}

\lipsum*[2] 
\end{document}

Although really I prefer the classic numeration at right of formulas, without captions. ;)

Answer 2

If you want to center normal text, one usually uses the center environment:

 \documentclass{article}
 \begin{document}
     \[ a^2+b^2=c^2 \]
     \begin{center}
         This is the Pythagorean Theorem.
     \end{center}
 \end{document}

If you insist on using centering, then make sure you put braces around your text, like {\centering This is the Pythagorean Theorem}.

Answer 3

Another possibility: use the gather environment (a multiline, centred, maths environment), and put the ‘caption’ on the second line:

\documentclass{article}

\usepackage{amsmath, amssymb}

 \begin{document}

\begin{gather}
   a\not\equiv 0\mod p \implies a^{p-1}\equiv 1\mod p \\
  \text{\small This is known as \emph{lil’Fermat}.}\notag
\end{gather}

 \end{document} 

Answer 4

If you include amsmath and want to center a single line, an easy solution can be to use \text{} into an equation:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
    \[ a^2+b^2=c^2 \]
    \[\text{This is the Pythagorean Theorem.}\]
    $$ \text{This is the Pythagorean Theorem.} $$
\end{document}

Answer 5

An easy way to do this is to use the switch command for the alignment you want. Here is an example of centering the text over a multicol environment and returning to justified text for the following content. There may be a better way, but I got errors trying to use a centering environment or a \par. The \justify command can also be placed just before \Blindtext.

\documentclass{report}
\usepackage{multicol}
\usepackage{ragged2e}
\usepackage{blindtext}
\begin{document}
\begin{multicols}{3}
[\centering Some over text\\justify
\rule{\textwidth}{0.4pt}
]
\Blindtext
\end{multicols}
\noindent\rule{\textwidth}{0.4pt}
\end{document}