[Tex/LaTex] How to have a single vertically centred equation number for multiline equation in LyX

equationslyxnumbering

I want a single equation number located between the second and third lines (vertically centered behind the lines):

as in Section 18.6 of the LyX detailed Math manual:

In Lyx, I choose "insert" → "Math" → "numbered formula", then right-lick the written equation to choose AMS align environment, and use \hspace and Ctrl+Space to adjust manually, but I get all lines numbered!

I try to delete the unwanted numbers by right clicking and unticking "number this line". This removed only the last number: the top three are still numbered, which is weird:

Best Answer

You should select first Insert/Math/Numbered Formula ("Formule numérotée" in my French version of Lyx), and then Insert/Math/Aligned Environment ("Environnement aligné" in French). If I export the resulting program to LaTeX, it contains the aligned environment.

\documentclass[english]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{luainputenc}
\usepackage{amsmath}
\usepackage{babel}
\begin{document}
\begin{equation}
\begin{aligned}1 & 2\end{aligned}
\end{equation}

\end{document}

Related Solutions

[Tex/LaTex] Tag placement in split equation within alignment block

I believe that assigning two equation numbers to one long equation First = line = Second line continued is a non-sense, and even if it makes sense, it will always confuse the reader. In my opinion, the correct solution is to First or line and put an explanatory line in between:

\begin{align}
  First ={}& line
\intertext{and by the Piegonhole principle}
  \begin{split}
    First ={}& Secondline % choose one of these two lines
%   line  ={}& Secondline % choose one of these two lines
  \\
  & continued
  ,\end{split}
\end{align}

Notice that you can use ={}& to place the alignment position after = and get the proper spacing.

enter image description here

(I decided to make the texts math-mode to 1st show how ugly it is and 2nd show that the spacing around the ='s is correct.)

As for the vertical alignment of the number, there's no real preference of one or the other. Just notice that if you put it on the bottom line and it's on the right, the correct left variant is on the top line.

\begin{align}
  First ={}& line
\intertext{and by the Piegonhole principle}
\nonumber  
  First ={}& Secondline % choose one of these two lines
% line  ={}& Secondline % choose one of these two lines
\\
  & continued
,\end{align}

[Tex/LaTex] How to label text with equation number

Here's one way (taken some code from Input manually a number into \eqref):

enter image description here

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/
\makeatletter
\newcommand{\eqnum}{\refstepcounter{equation}\textup{\tagform@{\theequation}}}
\makeatother
\begin{document}
\begin{equation}
  f(x) = ax^2 + bx + c \label{myeqn1}
\end{equation}
See~\eqref{myeqn1}. Also
\begin{itemize}
  \item $A$ is very~$b$, \eqnum\label{myeqn2}
  \item $A$ is not~$c$. \eqnum\label{myeqn3}
\end{itemize}
There is also~\eqref{myeqn2} and~\eqref{myeqn3}.
\end{document}

The above MWE provides \eqnum which inserts the equation number using the amsmath \eqref way. A subsequent \label makes one able to reference it. Of course, the print-and\label technique could be combined, if needed:

\makeatletter
\newcommand{\eqlab}[1]{\refstepcounter{equation}\label{#1}\textup{\tagform@{\theequation}}}
\makeatother

which allows one to use \eqlab{<label>}.

For flushed-right equation numbering, use the following definition:

\newcommand{\eqnum}{\leavevmode\hfill\refstepcounter{equation}\textup{\tagform@{\theequation}}}

Best Answer

Related Solutions

[Tex/LaTex] Tag placement in split equation within alignment block

[Tex/LaTex] How to label text with equation number

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