Equations alignment white space

Question

In the following excerpt, I would like to align the set of equations as indicated by the & or && symbols, except that I need the left-hand side of each equation to be attached to the = or \geq signs. In other words, I would like to have the horizontal white spaces just after the equation numbers.

Thank you in advance for any suggestions.

\documentclass{extbook}
\usepackage{amsmath}
\begin{document}
\begin{equation}
    \begin{aligned}
        &\textnormal{(i)} \enspace f'(x^) &&= \sum\limits_{i=1}^m \lambda_i h'i(x^*) +\sum\limits{i=1}^p \mu_i^* g'_i(x^) \
        &\textnormal{(ii)} \enspace h_i(x^) &&= 0, ; i=1,\ldots, , m, \
        &\textnormal{(iii)} \enspace g_i(x^) &&\ge 0, ; i=1, \ldots, , p, \
        &\textnormal{(iv)} \enspace \mu_i^ g_i(x^) &&=0, ; i=1,\ldots, , p, \
        &\textnormal{(v)} \enspace \mu_i^ &&\ge 0, ; i=1,\ldots, , p.
    \end{aligned}
\end{equation*}
\end{document}

score 3 · Answer 1 · answered Jul 14 '23 at 01:03

Use alignedat:

\documentclass{extbook}
\usepackage{amsmath}
\begin{document}
\begin{equation}
    \begin{alignedat}{2}
        &\textnormal{(i)} & f'(x^) &= \sum\limits_{i=1}^m \lambda_i h'i(x^*) +\sum\limits{i=1}^p \mu_i^* g'_i(x^) \
        &\textnormal{(ii)} & h_i(x^) &= 0, ; i=1,\ldots, , m, \
        &\textnormal{(iii)} & g_i(x^) &\ge 0, ; i=1, \ldots, , p, \
        &\textnormal{(iv)} & \enspace \mu_i^ g_i(x^) &=0, ; i=1,\ldots, , p, \
        &\textnormal{(v)} & \mu_i^ &\ge 0, ; i=1,\ldots, , p.
    \end{alignedat}
\end{equation*}
\end{document}

Werner · Accepted Answer · 2023-07-14T02:07:05.610

You just need to insert an additional & instead of \enspace in your aligned environment. However, it seems like you're interested in an enumeration of a list of elements, coupled with an alignment around the relations. For that, set each equation as an \item with some box measurement/manipulation to aid with the lefthand side alignment.

Both options are shown below:

\documentclass{article}
%\usepackage{showframe}
\usepackage{enumitem}
\usepackage{amsmath,eqparbox}
% https://tex.stackexchange.com/a/34412/5764
\makeatletter
\NewDocumentCommand{\eqmathbox}{o O{c} m}{%
  \IfValueTF{#1}
    {\def\eqmathbox@##1##2{\eqmakebox[#1][#2]{$##1##2$}}}
    {\def\eqmathbox@##1##2{\eqmakebox{$##1##2$}}}
  \mathpalette\eqmathbox@{#3}
}
\makeatother
\begin{document}
[
  \begin{aligned}
    &\textnormal{(i)}   &          f'(x^) &= \sum\limits_{i = 1}^m \lambda_i h'_i(x^) + \sum\limits_{i = 1}^p \mu_i^* g'_i(x^) \
    &\textnormal{(ii)}  &         h_i(x^) &= 0, ~ i = 1,\dots, m, \
    &\textnormal{(iii)} &         g_i(x^) &\geq 0, ~ i = 1, \dots, p, \
    &\textnormal{(iv)}  & \mu_i^ g_i(x^) &= 0, ~ i = 1, \dots, p, \
    &\textnormal{(v)}   &          \mu_i^ &\geq 0, ~ i = 1, \dots, p.
  \end{aligned}
]
\begin{enumerate}[label={(\roman)},align=left]
  \item
  $\displaystyle\eqmathbox[LHS][r]{f'(x^)} = \sum\limits_{i = 1}^m \lambda_i h'i(x^*) + \sum\limits{i = 1}^p \mu_i^* g'_i(x^*)$
\item
  $\eqmathbox[LHS][r]{h_i(x^*)} = 0, ~ i = 1,\dots, m$,
\item
  $\eqmathbox[LHS][r]{g_i(x^*)} \geq 0, ~ i = 1, \dots, p$,
\item
  $\eqmathbox[LHS][r]{\mu_i^* g_i(x^*)} = 0, ~ i = 1, \dots, p$,
\item
  $\eqmathbox[LHS][r]{\mu_i^*} \geq 0, ~ i = 1, \dots, p$.
\end{enumerate}
\end{document}

\eqmathbox[<tag>][<align>]{<stuff>} sets <stuff> in the widest box possible across all similar <tag>s, with additional <align>ment options (default is centred, but you can also align to the left or right).

Since eqparbox (used by \eqmathbox internally) measures its contents using a mechanism similar to what \label-\ref does (via the .aux), you'll have to compile at least twice with every change of the maximum width in some <tag> (necessarily also on the first compilation).

showframe was used to indicate the text block boundary (seen in the image as the black bars along the side).

Thank you, @Werner. I was also wondering how to align the set of equations to the left of the page. (Sorry, I should have probably asked that in the question.) — AEW, Jul 14 '23 at 01:13
@AEW: Do you still want a math display? Or do you really just want an enumerated list with elements in it, but the elements still aligned around the relations? — Werner, Jul 14 '23 at 01:24
I think I need the math environment to keep the equation alignment that you proposed. — AEW, Jul 14 '23 at 01:36
@AEW: It's not about what you think you need... what is it that you want? Here are the options, visually: image — Werner, Jul 14 '23 at 01:51

Equations alignment white space

2 Answers2