alignequations
I want to include a list of related equations, say, for a proof, in my LaTeX document. As far as I know, I have two good options, eqnarray and align.
What is the difference between eqnarray and align, and how do I know which I should be using? Or does it matter at all?
\documentclass[preview,border=12pt]{standalone}% please change to your document class
\usepackage{mathtools}
\usepackage{amsthm}
\newtheorem{mydef}{Definition}
\begin{document}
\begin{mydef}
\begin{align}
\text{distance} &= \text{speed} \times \text{time}\\
\intertext{and}
y &= \mathrm{m}x + \mathrm{c}
\end{align}
\end{mydef}
\begin{mydef}
\begin{align}
\mathrm{distance} &= \mathrm{speed} \times \mathrm{time}\\
\shortintertext{and}
y &= \mathrm{m}x + \mathrm{c}
\end{align}
\end{mydef}
\end{document}
Compare the results in the first and the second theorems carefully.
Use \text when you want its content to be affected by the surrounding font. For example, if \text is used inside a theorem environment, the surrounding font is italic so the contents of \text will be in italic as well.
Use \mathrm when you don't want its contents to be affected by the surrounding font.
\intertext for getting normal spacing but \shortintertext for shorter one.
Best Answer
Although
eqnarraymay seem to work "well enough", Avoid eqnarray! Avoid eqnarray! Avoid eqnarray!Two main problems are mentioned in the doc above:
eqnarraysets horizontal space around the=operator that is not consistent with the space set in other environments, such as\[...\]or$$...$$(it is wider).eqnarray(alsoeqnarray*!) has an ill-defined equation numbering, which leads to numbering errors on referencing—mostly when using the command\nonumberUse
alignand the rest of the ams environments. Seetexdoc amsldoc(PDF) or the short math guide for LaTeX for documentation on how to use them.