I always use align in my documents, and avoid equation. Is there anything wrong with that? My reasoning behind this: align > equation, so why not use it?
[Tex/LaTex] align vs equation
amsmathequations
Related Solutions
Cannot reprocude the problem, please post a full minimal example. This (using pmatrix works fine)
\documentclass[a4paper]{memoir}
\usepackage{amsmath}
\newcommand{\shat}[1]{\ensuremath{\hat{#1}}}
\begin{document}
\begin{align}
\begin{pmatrix}
\shat{X} \\
\shat{X}' \\
\shat{Y} \\
\shat{Y}' \\
\end{pmatrix}_{n+1}
= R(\omega_x, \omega_y)
\begin{pmatrix}
\shat{X} \\
\shat{X}' + \shat{X}^2 - \chi \shat{Y}^2 + \kappa \left( \shat{X}^3
- 3 \chi \shat{X} \shat{Y}^2 \right) \\
\shat{Y} \\
\shat{Y}' - 2 \chi \shat{X} \shat{Y} - \kappa \left( \chi^2
\shat{Y}^3 - 3 \chi \shat{X}^2 \shat{Y} \right) \\
\end{pmatrix}_n
\notag
\end{align}
\end{document}
You are incorrectly nesting structures, and the log file will contain error messages telling you this is happening.
equation already puts the contents in math mode, so $ and $$ are not needed nor allowed in its contents.
\documentclass{article}
\usepackage{amsmath}
\begin{document}
Text.
\begin{equation}
N(t) =
\frac{P_o}{\lambda+\rho\varepsilon/\Lambda}
[1-e^{-t(\lambda+\rho\varepsilon/\Lambda})]
\end{equation}
\end{document}
Similarly align is a top level command producing a displayed equation, but now with alignment points between lines (marked by &). If you need an align structure inside equation you should use aligned instead. See the documentation of amsmath for further information and examples.
Addendum Your original code has \textit{N}(\textit{t}) which as egreg points is almost certainly not what you intended. In math mode letters are automatically in an italic font (actually \mathit) and just writing N(t) as above will give you better spacing.
Best Answer
While not exactly a bad idea in principle, unfortunately it is a bad idea in practise because
aligndoesn't have the same feature asequationwhereby less vertical space is added if a small equation is displayed after a paragraph that ended early on the line. For example, considerYou should easily be able to see the extra space after the second ‘hello’.