To align equations, we use the align environment, and to use align environment, package amsmath
should be called.
this method uses \{split}
and ={}&
in a \align
environment to align equations
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
\begin{split}
equation1 ={}& ...
\end{split} \\
\begin{split}
equation2 ={}& ...
\end{split}\\
equation3 ={}& ...
\end{align}
\end{document}
Notes for this method:
\begin{align}
and \end{split}
{split}
environment.{}&
to equal sign of each equation: ={}&
\\
after each equation or \end{split}
\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
\begin{split}
g(x) ={}& 2[1-(1+x)exp(-x)]/x^2
\end{split}\\
g'(x) ={}& -2[1-(1+x+x^2/2)exp(-x)]/x^2
\end{align}
\end{document}
Different from method #1, replace ={}&
with &=
, and no need for split
environment:
\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
g(x) &= 2[1-(1+x)exp(-x)]/x^2\\
g'(x) &= -2[1-(1+x+x^2/2)exp(-x)]/x^2
\end{align}
\end{document}
also note:
\begin{split}
to \end{align}
\\
to make line breaks&
to each equal sign of equationsActually, in above examples, we have at least two conditions to be considered:
If you don't want equations to be numbered, you just need add a *
symbol to the {align}
environment, that is:
\begin{align*}
[content...]
\end{align*}
this works for both of the methods mentioned above. The rest elements between `\begin{align*}` and `\end{align*}`are all the same as above numbered alignment.
---
Long equations in latex will arise several problems, so here we treat long equations specially.
For long equations, we have to use \\
to make new lines so that the whole equation can be displayed properly. However, this action also cause our single equation be numbered duplicately:
to solve this problem, we use a \nonumber
mark at the end of lines and before the line break mark \\
, except for the one we want the number be displayed at (often the last line):
\begin{align}
[line1...] \nonumber \\
[line2...] \nonumber \\
[line3...] % show number at this line
\end{align}
now, duplicate numbers disappear.
Next, we will adjust the alignment to make the display of the number more proper.
Alignment of equations in former sections are based on the equal sign =
, different equations can be aligned along the vertical line of "=". However, for long equations, how do we adjust multiple lines of a single equation when there is only one equal sign?
Based on last example, we use two key marks to align a long equation with line breaks:
&=
\mathrel{phantom{=}}
\phantom{}
: is used to make space, phantom{=}
means make a space of which the width is equal to a =
sign.\mathrel{}
: make relation spacing.syntax:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
[left] &= [line1...] \nonumber \\
&\mathrel{\phantom{=}} [line2...] \nonumber \\
&\mathrel{\phantom{=}} [line3...] % show number at this line
\end{align}
\end{document}
now, the example equation has a good appearance:
&
sign before \mathrel
In some cases we need to use equal sign multiple times in a single equation, how do we align the equation then?
Since there are equal sign in each line, so the alignment would be easily base on the equal sign again:
syntax:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
[left] &= [line1...] \nonumber \\
&= [line2...] \nonumber \\
&= [line3...] % show number at this line
\end{align}
\end{document}
(note: the example is a fake equation).