[Tex/LaTex] Subequations inside align result in too wide equation

alignhorizontal alignmentsubequations

I want to create subequations and allign them such that nice 'inquality constraints' arise. My current code:

\begin{subequations}
\begin{align}
a & \le b & \le c \label{eq:constr1}\\
d & \le effff & \le f \label{eq:constr1}\\
\end{align}
\label{eq:constr}%
\end{subequations}

The result in PDF is a much too large distance between "b and c" and "efffff and f". I would like to have \le exactly below eachother. Have b and effff centered between those. Finally a and d should be right aligned to the \le and c and f should be left aligned to the \le.

Best Answer

If you want the middle column to be centered than you need to either resort to using a \makebox to reserve enough width for that column, which requires knowing what the widest element is beforehand, or to use an array:

enter image description here

Notes

The alignat provides pairs of rl aligned equations. Since we want the third column to be left aligned, we need to use a && to skip past the prior column that would have been right aligned.
For the array solution we need to use {} to make the inequality symbols be treated as relational operators, similar to the difference in spacing of $-x$ and ${}-x$ .
The calc package was used for the \widthof{} macro, so is only required for the alignat solution.
As Qrrbrbirlbel commented, you could make use of the array package and incorporate the required {} into the column specification, as shown in the last example in the code below.

Code:

\documentclass{article}
\usepackage{amsmath}
\usepackage{calc}
\usepackage{array}

\newcommand*{\Widest}{effff}%
\newcommand*{\WideAs}[1]{\makebox[\widthof{$\Widest$}][c]{$#1$}}%
\begin{document}\noindent
You can use \verb|alignat|:
%
\begin{alignat*}{3}
    a & \le \WideAs{b}     && \le c \\
    d & \le \WideAs{effff} && \le f 
\end{alignat*}
%
Or use \verb|array|:
%
\[\begin{array}{r@{}c@{}l}
    a \le {}& b     &{} \le c \\
    d \le {}& effff &{} \le f 
\end{array}\]
%
Alternatively using the \verb|array| package:
\[\begin{array}{r<{{}}@{}c@{}>{{}}l}
    a \le & b     & \le c \\
    d \le & effff & \le f 
\end{array}\]
\end{document}

Related Solutions

[Tex/LaTex] Aligning multiple rows and columns with different number of equations (Align environment)

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  &  &  &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \begin{aligned}
         x3&=y3 \\
         a3&=b3
        \end{aligned}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  & \qquad\qquad & \qquad\qquad &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \mathclap{\begin{aligned}
         x3&=y3 \\
         a3&=b3
        \end{aligned}}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

The long third equation version:

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  & \qquad\qquad & \qquad\qquad &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \mathclap{\begin{aligned}
         x3&=y3 +a1 -d1 +e5 +a1 -d1 +e5 \\
         a3&=b3
        \end{aligned}}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

The centered long third equation version:

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  & \qquad\qquad & \qquad\qquad &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \mathclap{\begin{gathered}
         x3=y3 +a1 -d1 +e5 +a1 -d1 +e5 \\
         a3=b3
        \end{gathered}}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

[Tex/LaTex] flush text on the left and centre equation of the same line (not working!)

Here are three possibilities; the first two are variants based on the flalign environment, with a different positioning of the equations w.r.t.the left margin text. The third possibility paves the texts aligned w.r.t. each other, at some distance from the equations. It's based on alignat:

\documentclass[a4paper, 12pt, default, numbered, print, index]{article}
\usepackage{mathtools}

\usepackage{eqparbox} \newcommand{\eqmathbox}2[M]{\eqmakebox[#1]{$\displaystyle#2$}}

\DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
\DeclareFontShape{U}{mathx}{m}{n}{
<5><6><7><8><9><10>
<10.95><12><14.4><17.28><20.74><24.88>
mathx10
}{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}
\DeclareFontSubstitution{U}{mathx}{m}{n}
\DeclareMathAccent{\widebar}{0}{mathx}{"73}

\begin{document}

We can simplify our analysis by assuming the flow is inviscid ($\tau_{i,j}$ = 0), an ideal gas ($p = ρRT$), and calorically perfect ($c_p$, $c_v$ = constant). Thus, for a homogeneous, steady, uniform gas flow in a straight duct without heat conduction, the linearised governing equations can be written as:

\begin{subequations}
\begin{flalign}
\label{eq:linear_EOM_vector_mass}
 & \rlap{Mass} & &\eqmathbox{\frac{\widebar{D}\rho'}{Dt} + \bar{ρ}∇ · \boldsymbol{u}' = \mathbf{0}} & \\[0.8ex]
\label{eq:linear_EOM_vector_mom}
 & \rlap{Momentum} & &\eqmathbox{\frac{\widebar{D}\mathbf{u}'}{Dt} + \frac{1}{\bar{ρ}}
∇ p' = \mathbf{0}}
\end{flalign}
\end{subequations}

\begin{subequations}
\begin{flalign}
\label{eq:linear_EOM_vector_mass}
 & \text{Mass} & & \frac{\widebar{D}\rho'}{Dt} + \bar{ρ}∇ · \boldsymbol{u}' = \mathbf{0} &\hspace{12em} \\[0.8ex]
\label{eq:linear_EOM_vector_mom}
 & \text{Momentum} & & \frac{\widebar{D}\mathbf{u}'}{Dt} + \frac{1}{\bar{ρ}}
∇ p' = \mathbf{0}&&
\end{flalign}
\end{subequations}

\begin{subequations}
\begin{alignat}{2}
\label{eq:linear_EOM_vector_mass}
 & \text{Mass} &\hspace{3em} &\frac{\widebar{D}\rho'}{Dt} + \bar{ρ}∇ · \boldsymbol{u}' = \mathbf{0} \\[0.8ex]
\label{eq:linear_EOM_vector_mom}
 & \text{Momentum} & & \frac{\widebar{D}\mathbf{u}'}{Dt} + \frac{1}{\bar{ρ}}
∇ p' = \mathbf{0}
\end{alignat}
\end{subequations}

\end{document}

Edit: Here is how to adapt the first solution to the last version of the O.P.'s code (two variants):

\documentclass[a4paper,12pt,default,numbered,print,index]{article}
\usepackage{lipsum}
\usepackage{enumitem}
\usepackage{graphicx} % Required for the inclusion of images
\usepackage{setspace} % for use of \singlespacing and \doublespacing
\usepackage{pdfpages}
\usepackage{cite}
\usepackage[section]{placeins}
\usepackage{comment}
\usepackage{siunitx}
\usepackage{color}
\usepackage{ragged2e}
\usepackage{esvect}
\usepackage{mathtools}
\usepackage{lscape}
\usepackage{tabularx}
\usepackage{multirow}
\usepackage{array}
\usepackage{soul}
\usepackage{bm}
\usepackage{url}
\usepackage{xparse}
\usepackage{hyperref}
\newcommand{\myeqlabel}[1]{\rlap{\bfseries#1}}
\usepackage{eqparbox}
\newcommand{\eqmathbox}[2][M]{\eqmakebox[#1]{$\displaystyle#2$}}

    \DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
    \DeclareFontShape{U}{mathx}{m}{n}{
    <5><6><7><8><9><10>
    <10.95><12><14.4><17.28><20.74><24.88>
    mathx10
    }{}
    \DeclareSymbolFont{mathx}{U}{mathx}{m}{n}
    \DeclareFontSubstitution{U}{mathx}{m}{n}
    \DeclareMathAccent{\widebar}{0}{mathx}{"73}


\begin{document}

We can simplify our analysis by assuming the flow is inviscid ($\tau_{i,j} = 0$), an ideal gas ($p = \rho RT$), and calorically perfect ($c_p$, $c_v$ = constant). Thus, for a homogeneous, steady, uniform gas flow in a straight duct without heat conduction, the linearised governing equations can be written as:
\begin{subequations}
\begin{flalign}
& \myeqlabel{Mass} &&
    \eqmathbox{\frac{\widebar{D}\rho'}{Dt} + \bar{\rho}\,\nabla\cdot\boldsymbol{u}'
            = \mathbf{0}} & \label{eq:linear_EOM_vector_mass}\\
& \myeqlabel{Momentum} &&
    \eqmathbox{\frac{\widebar{D}\mathbf{u}'}{Dt} + \frac{1}{\bar{\rho}} \nabla p'
            = \mathbf{0}} & \label{eq:linear_EOM_vector_mom}\\
& \myeqlabel{Energy} && 
    \eqmathbox{c_p\frac{\widebar{D}}{Dt}(\bar{\rho}\,T' + \rho'\widebar{T}) + \nabla \cdot (\boldsymbol{u'}\bar{p} + \bar{\boldsymbol{u}}p')
            = \dot{q}'\bar{\rho} + \bar{\dot{q}}\rho' }& \label{eq:linear_EOM_vector_energy}\\
& \myeqlabel{Entropy} && 
    \eqmathbox{\frac{\widebar{D}s'}{Dt}
            = \frac{\dot{q}'}{\bar{\rho}\,\bar{T}}} & \label{eq:linear_EOM_vector_entropy}\\
& \myeqlabel{Vorticity} &&
    \eqmathbox{\frac{\widebar{D}\boldsymbol{\xi}'}{Dt}
            = \mathbf{0}} & \label{eq:linear_EOM_vector_vorticity}
\end{flalign}
\end{subequations}
\begin{subequations}
\begin{flalign}
& \myeqlabel{Mass} &&
    \eqmathbox{\frac{\widebar{D}\rho'}{Dt} + \bar{\rho}\,\nabla\cdot\boldsymbol{u}'
            = \mathbf{0}} & \label{eq:linear_EOM_vector_mass}\\
& \textbf{Momen\rlap{tum}} &&
    \eqmathbox{\frac{\widebar{D}\mathbf{u}'}{Dt} + \frac{1}{\bar{\rho}} \nabla p'
            = \mathbf{0}} & \label{eq:linear_EOM_vector_mom}\\
& \myeqlabel{Energy} &&
    \eqmathbox{c_p\frac{\widebar{D}}{Dt}(\bar{\rho}\,T' + \rho'\widebar{T}) + \nabla \cdot (\boldsymbol{u'}\bar{p} + \bar{\boldsymbol{u}}p')
            = \dot{q}'\bar{\rho} + \bar{\dot{q}}\rho' }& \label{eq:linear_EOM_vector_energy}\\
& \myeqlabel{Entropy} &&
    \eqmathbox{\frac{\widebar{D}s'}{Dt}
            = \frac{\dot{q}'}{\bar{\rho}\,\bar{T}}} & \label{eq:linear_EOM_vector_entropy}\\
& \myeqlabel{Vorticity} &&
    \eqmathbox{\frac{\widebar{D}\boldsymbol{\xi}'}{Dt}
            = \mathbf{0}} & \label{eq:linear_EOM_vector_vorticity}
\end{flalign}
\end{subequations}

\end{document}

Best Answer

Notes

Code:

Related Solutions

[Tex/LaTex] Aligning multiple rows and columns with different number of equations (Align environment)

[Tex/LaTex] flush text on the left and centre equation of the same line (not working!)

Related Question