[Tex/LaTex] the difference between aligned in displayed mode and starred align

alignamsmath

I am confused in choosing one of the following approaches.

\documentclass{article}
\usepackage{siunitx}
%\sisetup{detect-all}
\usepackage{amsmath}
\parindent=0pt\relax
\begin{document}
The following calculation is a trivial example
\[
\begin{aligned}
q       &=CV                                \\
        &=\num{3e-20x1000}  \\
        &=\num{3e-17}
\end{aligned}
\]
The following calculation is a trivial example
\begin{align*}
q       &=CV                                \\
        &=\num{3e-20x1000}  \\
        &=\num{3e-17}
\end{align*}

\end{document}

What is the difference between aligned in displayed mode and starred align?

Edit:

If there is a difference and we have to show the substitution steps above or algebraic operation steps below, which one we have to use based on the internationally adopted convention?

\documentclass{article}
\usepackage{amsmath}

\begin{document}
The following calculation is a trivial example
\[
\begin{aligned}
a(x+b)^2 - ab^2 &= a(x^2 + 2bx + b^2) - ab^2\\
                                &= ax^2 + 2abx + ab^2 - ab^2\\
                                &= ax^2 + 2abx
\end{aligned}
\]

The following calculation is a trivial example
\begin{align*}
a(x+b)^2 - ab^2 &= a(x^2 + 2bx + b^2) - ab^2\\
                                &= ax^2 + 2abx + ab^2 - ab^2\\
                                &= ax^2 + 2abx
\end{align*}

\end{document}

Best Answer

Your first version is essentially a single equation (that contains several lines of aligned equations, but that is secondary). Your second version consists of several equations. This alters the spacing above and below that:

\documentclass{article}
\usepackage{amsmath}
\parindent=0pt\relax
\begin{document}
The following calculation is a trivial example
\hrule
\[
\begin{aligned}
q       &=CV                                \\
        &=3e-20x1000  \\
        &=3e-17
\end{aligned}
\]
\hrule

\bigskip

\hrule
\begin{align*}
q       &=CV                                \\
        &=3e-20x1000  \\
        &=3e-17
\end{align*}
\hrule
\end{document}

yields: display math versus align

Usually you want the larger spacing around a block of several equations. Your second version is also conceptually clearer.

Related Solutions

[Tex/LaTex] What’s the difference between align and align*

The star at the end of the name of a displayed math environment causes that the formula lines won't be numbered. Otherwise they would automatically get a number.

You can read about that in the amsmath user's guide since align belongs to amsmath.

Such information can usually be found in the package documentation. Type texdoc packagename at the command prompt or visit http://ctan.org/pkg/packagename. If you use google or another search engine, look for starred and commandname.

Commonly, a star symbol * means a version of a command that behaves differently from the original. That often means suppressing numbering but could also refer to special features. For example, have a look at What's the difference between \newcommand and \newcommand*?

[Tex/LaTex] Difference between (split, align) and (gather, aligned)

For the example alignment the following are equivalent; actually, the correct outer environment to use is equation, as the following code will show; using split or aligned for the inner environment in this case doesn't matter.

\documentclass{article}
\usepackage{amsmath,lipsum,geometry}
\geometry{margin=1cm}
\begin{document}
%\thispagestyle{empty}

\lipsum*[2]
%==================
% equation+aligned
\begin{equation}\tag{EA}
\begin{aligned}
x &= a + b\\
y &= c+ d
\end{aligned}
\end{equation}
\lipsum*[2]
%==================
% equation+split
\begin{equation}\tag{ES}
\begin{split}
x &= a + b\\
y &= c+ d
\end{split}
\end{equation}
\lipsum*[2]
%==================
% gather+aligned
\begin{gather}\tag{GA}
\begin{aligned}
x &= a + b\\
y &= c+ d
\end{aligned}
\end{gather}
\lipsum*[2]
%==================
% gather+split
\begin{gather}\tag{GS}
\begin{split}
x &= a + b\\
y &= c+ d
\end{split}
\end{gather}
\lipsum*[2]
%==================
% align+split
\begin{align}\tag{AS}
\begin{split}
x &= a + b\\
y &= c+ d
\end{split}
\end{align}
\lipsum*[2]
%==================
% align+aligned
\begin{align}\tag{AA}
\begin{aligned}
x &= a + b\\
y &= c+ d
\end{aligned}
\end{align}
\lipsum*[2]

\end{document}

In the output it's possible to see that the correct spacing is obtained with equation. Use align or gather only when there is really more than one equation to number.

One should also note that "equation+split" results in a different vertical spacing than "equation+aligned" (which isn't really expected).

enter image description here

Best Answer

Related Solutions

[Tex/LaTex] What’s the difference between align and align*

[Tex/LaTex] Difference between (split, align) and (gather, aligned)

Related Question