Aligning formulas inside enumerate

Question

I have an ordered list (enumerate) each item of which is a numbered formula. I am using a gather environment.

\documentclass[12pt,a4paper]{article}
\usepackage[T2A]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{amsmath}
\begin{document}
The following conditions are true:
\begin{enumerate}
\item \begin{gather}
    x^2 \ge 0,
\end{gather}
\item \begin{gather}
    x^2 \ge 0,
\end{gather}
\end{enumerate}
\end{document}

But the formulas appear in the center of the next line producing one empty line.

How can I get rid of the empty lines and align the formulas to the left? Formula numbers must stay on the right. I would like to stick to the gather environment if possible, because I find it very convenient for my purposes.

@Skillmon: There might be text in addition to an equation in each item, and the list numbering might be independent of the equation numbering. — Bernard, Aug 14 '18 at 12:00
@Bernard, I use other languages apart from English as well. This is just a MWE. — user2513149, Aug 14 '18 at 12:39
this question might be helpful: Equations inside enumerate aligned on item's number (possible duplicate) — barbara beeton, Oct 01 '18 at 13:12

Bernard · Accepted Answer · 2018-08-14T14:50:28.563

5

Here is a solution: I define a new environment, Lgather (L is for both list and left), with the help of package nccmath, which defines a fleqn environment (inside this environment, equations are left-aligned) and a \useshortskip command, which in practice makes the spacing between text and displayed equation equal to \baselineskip, so I only had to neutralise it with a \vspace*{-\baselineskip}.

\documentclass[12pt, a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{amsmath, nccmath}
\newenvironment{Lgather}{\useshortskip\leavevmode\vspace*{-\baselineskip}\fleqn\gather}{\endgather\endfleqn}

\begin{document}

The following conditions are true:
\begin{enumerate}
    \item 
    \begin{Lgather}
    x^2 \ge 0,
 \end{Lgather}
\item 
    \begin{Lgather}
    x^2 \ge 0,
    \end{Lgather}
\end{enumerate}

\end{document}

edited Aug 14 '18 at 14:50

answered Aug 14 '18 at 11:53

Bernard

271,350

Brillant but coding is not understandable by plain Latex users. – pzorba75 Aug 14 '18 at 14:36
1

@pzorba75: I've added an explanation for \useshortskip. Is it clearer? – Bernard Aug 14 '18 at 14:51
@Bernard : For sure, this explanation is useful. But I still remain unable to write such expressions from my own. – pzorba75 Aug 14 '18 at 17:10
2

@pzorba75 \newenvironment lets you define a new environment it takes 3 mandatory arguments being the environment's name, the code to be executed at \begin and the code to be executed at \end. The \begin part issues \useshortskip and a negative vertical skip of one \baselineskip. After that it starts two environments without using \begin namely fleqn and gather, both are ended in the end branch with \endfleqn and \endgather (the code to be used at \begin is stored in a macro with the environment's name as its name, the \end in \end<name>). – Skillmon Aug 14 '18 at 17:25
@pzorba75 does that help? – Skillmon Aug 14 '18 at 17:25
@Skillmon : Sure it helps; Why gather following fleqn is needed as there is only a one line expression in fleqn? – pzorba75 Aug 15 '18 at 03:41
@pzorba75 because fleqn is not a math environment but an environment in which every display math environment should be left aligned. You could use equation instead of gather for example, but you need to use a math environment. – Skillmon Aug 15 '18 at 06:33

Aligning formulas inside enumerate

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