How to align / count equation labels in Latex

Question

I am attempting to write a simple equation inside a document that uses Latex, and I have attempting this line of code so far:

\setcounter{equation}{0}
\renewcommand{\theequation}{1.\arabic{equation}\label{}}
\begin{equation}
\begin{center}
$\mathcal{L}= -\frac{1}{4}  \mathcal{F}_{\mu \nu} \mathcal{F}^{\mu \nu} \\
+ \mathcal{i} \overline{\psi} \cancel{D}\psi + h.c. \\
+ \overline{\psi}_i y_{ij} \psi_j \phi + h.c. 
\\
+|D_\mu \phi|^2 - V(\phi)$
\end{equation}
\end{center}

This gives me:

where the label is immediate to the equation.

I have attempted \setcounter \label \usepackage{amsmath} \begin{align*}, but to no avail. The equation number continues to be at the very end of this equation, where I would like it to be right aligned (at the right edge of the page). Any advice would be greatly appreciated.

Answer 1

You have errors in your code:

• $...$ and \[...\] opens/closes math environments
  • It is the error to use them inside an already created math environments
  • $...$ is for inline equations (equivalent but preferable form in LaTeX is \(...\))
  • \[...\] is a shot form for \begin{equation*}...\end{equation*} and is used for quick single-lined equations in display mode without eq. number
• Don't use any form of centring inside math anvironments
• More complex formatting requires other environments e.g. gather, align, alignat
  • Each such environment has an equivalent inner form: aligned, alignedat, and gathered
  • Inner forms can only be used inside already created math environment
  • Each of the inner form produces a single equation number, regardless of a number of lines it contains.

Also, a preferable way to make a section or a chapter number a part of the equation number is to use the following macro defined in amsmath:

\numberwithin{equation}{section}

It will reset the equation part every time you start a new section. Change section to chapter and you will get the same effect with chapters.

Here is one way to format your equation with a single equation number. The [b] is an optional argument of aligned environment to place eq. number at the bottom of the inner block.

More can be found in the documentation of amsmath package.

\documentclass{article}
\usepackage{amsmath}
\usepackage{cancel}

\numberwithin{equation}{section}

\begin{document}
\section{The first section}

\begin{equation}\label{eq:example}
  \begin{aligned}[b]  % change to [t], [c] if top- or middle-aligned, respectively
    \mathcal{L} &= -\frac{1}{4}  \mathcal{F}_{\mu \nu} \mathcal{F}^{\mu \nu} \\
    &\qquad + \mathcal{i} \overline{\psi} \cancel{D}\psi + h.c. \\
    &\qquad + \overline{\psi}?_i y_{ij} \psi_j \phi + h.c.\\
    &\qquad + |D_\mu \phi|^2 - V(\phi)
  \end{aligned}
\end{equation}

Reference to the Equation~\ref{eq:example}.
\end{document}

Answer 2

Do not ignore LaTeX errors. They are there for a reason

In your case, I notice that you have

\begin{equation}
   \begin{center}
      ...
   \end{equation}
\end{center}

(I added indentation to make it clear what’s happening). You have \begin{center} ended with \end{equation} and \begin{equation} ended with \end{center}.

You need to properly nest things.

And

you don’t want to use a center environment in the first place. And the $…$ shouldn’t be there.

When you have a multiline equation, you should use split from the amsmath package,¹ so your equation would look like

\begin{equation}
  \begin{split}
    \mathcal{L} = … \\
       … \\
       … \\
       …
  \end{split}
\end{equation}

---

1. If you’re unfamiliar with packages, this means that you will want to add to your document’s preamble (the stuff between \documentclass{…} and \begin{document}), the command:

   \usepackage{amsmath}
   

   You can find out more about the capabilities of the amsmath package by typing texdoc amsmath at a command line if you're running LaTeX on your computer or going to https://texdoc.org and typing amsmath into the search box there.