[Tex/LaTex] Left and centre alignment when using subequation and align environments

alignhorizontal alignmentsubequations

I have {amsmath},{amssymb} packages. The code :

\begin{subequations}
\begin{align}
u_0(x) = \frac{x} {y (x-b)^2 + z} ,  \qquad \qquad  \qquad \qquad \\
u_1(x) = \frac{-2 (m + n  + k)}{y (x-b)^2 + z} + \frac{a+b+c+d+e+f+g+h+j+k+l+m+n+ .... (let us make it so long) }{x+y+z} .
\end{align}
\end{subequations}

Well, the point is one of the subequations is so long comparing to the other.

What I need are;

(1) Centre all subequautions (without using \qquad or \quad).

(2) Align left all sub equations (without using \qquad or \quad).

Also, I need to tag each equation such as (a,b) (automatically not manually tagging).

Tried to use {gathered}, {alignat} and {aligned} environments with different context. But, it seems to me they do not provide all the conditions I have. Any proper way will be highly appreciated!

Best Answer

With environment align you need to add ampersands, which determine, where equations are aligned (usually at equal sign). Below are two cases of taging of your equation. See, if one is what you after:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{subequations}
\begin{align}
u_0(x) & = \frac{x} {y (x-b)^2 + z} ,               \label{eq:1a} \\
u_1(x) & = \frac{-2 (m + n  + k)}{y (x-b)^2 + z} .  \label{eq:1b}
\end{align}
\end{subequations}
or
\begin{align}
u_0(x) & = \frac{x} {y (x-b)^2 + z} ,               \label{eq:a}\tag{a} \\
u_1(x) & = \frac{-2 (m + n  + k)}{y (x-b)^2 + z} .  \label{eq:b}\tag{b}
\end{align}
See \eqref{eq:1a} and \eqref{eq:1b} or \eqref{eq:a} and \eqref{eq:b} \dots\\[1em] 
\textbf{Addendum}: with environment  'gather` equations are centered:
\begin{gather}
u_0(x) = \frac{x} {y (x-b)^2 + z} ,               \label{eq:c}\tag{c} \\
u_1(x) = \frac{-2 (m + n  + k)}{y (x-b)^2 + z} .  \label{eq:d}\tag{d}
\end{gather} 
\end{document}

Related Solutions

[Tex/LaTex] Alignment of equals sign in multiple align environments

From the amsmath documentation:

The command \intertext is used for a short interjection of one of two lines of text in the middle of a multiple-line display structure ... Its salient feature is preservation of the alignment, which would not happen if you simply ended the display and then started it up again afterwards. \intertext may only appear right after a \\ or \\* command.

So your example would be:

\begin{align*}
  foo &= something very very long compared to the other align \\
\intertext{explanation what I shall do now}
  foo' &= foo + short
\end{align*}

The breqn package also has this capability via its dsuspend environment.

(Added in edit) From the comments, there appear to be a few different ways to achieve this effect. So to help with choosing, here's a sample of all those that I'm aware of. Anyone who knows more is welcome to either add directly to this answer or to make a comment and then I'll add it. Here's the result:

variations on a theme of intertext

and here's the code that produced it:

\documentclass{article}
\thispagestyle{empty}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{breqn}

\begin{document}

\paragraph{Two aligns}

\begin{align*}
\begin{vmatrix}
a & b & c \\
d & e & f \\
g & h & i
\end{vmatrix}
&= a e i + b f g + c d h - a f h - b d i - c e g
\end{align*}
%
Whilst for \(2 \times 2\) we have:
%
\begin{align*}
\begin{vmatrix}
a & b \\
c & d
\end{vmatrix}
&= a d - b c
\end{align*}

\paragraph{One align, intertext preceeded by \textbackslash\textbackslash} 

\begin{align*}
\begin{vmatrix}
a & b & c \\
d & e & f \\
g & h & i
\end{vmatrix}
&= a e i + b f g + c d h - a f h - b d i - c e g \\
%
\intertext{Whilst for \(2 \times 2\) we have:}
%
\begin{vmatrix}
a & b \\
c & d
\end{vmatrix}
&= a d - b c
\end{align*}

\paragraph{One align, intertext not preceeded by \textbackslash\textbackslash} 

\begin{align*}
\begin{vmatrix}
a & b & c \\
d & e & f \\
g & h & i
\end{vmatrix}
&= a e i + b f g + c d h - a f h - b d i - c e g
%
\intertext{Whilst for \(2 \times 2\) we have:}
%
\begin{vmatrix}
a & b \\
c & d
\end{vmatrix}
&= a d - b c
\end{align*}

\paragraph{One align, shortintertext (mathtools)}

\begin{align*}
\begin{vmatrix}
a & b & c \\
d & e & f \\
g & h & i
\end{vmatrix}
&= a e i + b f g + c d h - a f h - b d i - c e g
%
\shortintertext{Whilst for \(2 \times 2\) we have:}
%
\begin{vmatrix}
a & b \\
c & d
\end{vmatrix}
&= a d - b c
\end{align*}

\paragraph{Using dsuspend from breqn}
~

\begin{dgroup*}
\begin{dmath*}
\begin{vmatrix}
a & b & c \\
d & e & f \\
g & h & i
\end{vmatrix}
= a e i + b f g + c d h - a f h - b d i - c e g
\end{dmath*}
\begin{dsuspend}
Whilst for \(2 \times 2\) we have:
\end{dsuspend}
\begin{dmath*}
\begin{vmatrix}
a & b \\
c & d
\end{vmatrix}
= a d - b c
\end{dmath*}
\end{dgroup*}


\end{document}

[Tex/LaTex] Subequation aligning using matrix

You can't use equation within align, so just remove all those, add & before the equals signs, and add a line break (\\) at the end of the first line (after the matrix) and this works just fine.

\documentclass[]{report}   % list options between brackets
\usepackage{amsmath} %contains the advanced math extensions for LaTeX

\begin{document}

\begin{subequations}
\begin{align}
 \label{eq:model_m}
    [X] &=
    \begin{bmatrix}
    a & 0 \\
    0 & b \\
    \end{bmatrix} \\
 \label{eq:model_c}
    [Y] &=
    \begin{bmatrix}
    c+e & 0\\
    0 & d+f
    \end{bmatrix}
\end{align}
\end{subequations}

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Alignment of equals sign in multiple align environments

[Tex/LaTex] Subequation aligning using matrix

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