Long formula in align environment

Question

Usually, if I have a very long formula, I will use two lines in the align environment and \qquad to space things out nicely. For example,

\begin{align*}
% First line
\rho\left(\frac{\partial u_{r}}{\partial t}+u_{r}\frac{\partial u_{r}}{\partialr}+\frac{u_{\phi}}{r}\frac{\partial u_{r}}{\partial\phi}+u_{z}\frac{\partial u_{r}}{\partial z}-\frac{u_{\phi}^{2}}{r}\right) & =-\frac{\partial p}{\partial r}+\mu\Biggl[\frac{1}{r}\frac{\partial}{\partial r}\left(r\frac{\partial u_{r}}{\partial r}\right)+\frac{1}{r^{2}}\frac{\partial^{2}u_{r}}{\partial\phi^{2}}
\\
% Second line
& \qquad\qquad\qquad\qquad
+\frac{\partial^{2}u_{r}}{\partial z^{2}}-\frac{u_{r}}{r^{2}}-\frac{2}{r^{2}}\frac{\partial u_{\phi}}{\partial\phi}\Biggr]+\rho g_{r}
\end{align*}

produces

However, this method of alignment is tedious, and not offsetting the second line usually results in something that looks poor. Is there an environment which facilitates this automatically?

Answer 1

I think using multline* instead of align* is the right way to go in these cases:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{multline*}
\rho\left(\frac{\partial u_{r}}{\partial t}+u_{r}\frac{\partial u_{r}}{\partial r}+
\frac{u_{\phi}}{r}\frac{\partial u_{r}}{\partial\phi}+u_{z}\frac{\partial u_{r}}{\partial z}-
\frac{u_{\phi}^{2}}{r}\right)=\\
-\frac{\partial p}{\partial r}+
\mu\Biggl[\frac{1}{r}\frac{\partial}{\partial r}\left(r\frac{\partial u_{r}}{\partial r} \right)+
\frac{1}{r^{2}}\frac{\partial^{2}u_{r}}{\partial\phi^{2}}+
\frac{\partial^{2}u_{r}}{\partial z^{2}}-\frac{u_{r}}{r^{2}}-
\frac{2}{r^{2}}\frac{\partial u_{\phi}}{\partial\phi}\Biggr]+\rho g_{r}
\end{multline*}
\end{document}