Math & Science ⇒ Equation Alignment causes several Errors

[Wenneguen]

Hello,

LaTeX tells me there are 12 errors in there :

Code: Select all

\begin{aligned}
  $|a_n| \sim |b_n| &\iff |a_n| - |b_n| = o(|a_n|) \\
&\iff \forall \varepsilon > 0, \exists N \in \mathbb{N}, \forall n \ge N, |a_n| - |b_n| \le \varepsilon |a_n|$
\end{aligned}

I guess it is because of the stuff in the aligned environment, since it is the first time I use it. Could someone explain how to use it so that LaTeX does not detect errors ? (surprisingly LaTeX displays exactly what I want to make, but I like documents without errors :D)

Thank you ! :)

[localghost]

Please always provide a self-contained and minimal example to make a problem comprehensible at all. This would also prevent others from guesswork and random shots.

The aligned environment only works in math mode, either in-line or display mode. Since you didn't provide a full example, one can only guess that you are perhaps looking for something like this.

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}  % loads »amsmath«

\begin{document}
  \begin{equation}
    \begin{aligned}
      |a_n| \sim |b_n| &\iff |a_n| - |b_n| = o(| :D a_n|) \\
      &\iff \forall \varepsilon > 0, \exists N \in \mathbb{N}, \forall n \ge N, |a_n|-|b_n| \le \varepsilon |a_n|
    \end{aligned}
  \end{equation}
\end{document}

And it's not necessary to activate in-line math mode ($…$) inside another math environment.


Further reading:

• The amsmath manual
• The »Math mode« document

Best regards and welcome to the board
Thorsten