Problem with using multline and align

I am LaTeX begginer and when I run this equation, I am getting the error:

! Argument \align* has an extra {.


Here is the equation.

\begin{multline}
\begin{align*}
C_s & = \displaystyle \max_{P(g_M)} \int_0^{\infty}
\bigg[ \left(1-\exp\left(-\frac{g_M}{\overline{g}_W}\right) \right)
\log\left(1+\frac{g_MP(g_M)}{N_M}\right)- \\
\int_0^{g_M} \log\left(1+\frac{g_WP(g_W)}{N_W}\right)
\frac{1}{\overline{g}_W}\exp\left(-\frac{g_W}{\overline{g}_W}\right)
dg_W \bigg]
\frac{1}{\overline{g}_W}\exp\left(-\frac{g_M}{\overline{g}_M}\right) dg_M \\
& = \max_{P(g_M)} \int_0^{\infty}
\bigg[\log \left(1+\frac{g_MP(g_M)}{N_M}\right) -
\exp\left(\frac{1}{\overline{g}_WP(g_M)}\right)
\bigg(Ei\left(\frac{1}{\overline{g}_WP(g_M)}\right)- \\
Ei\left(\frac{g_M}{\overline{g}_W}+
\frac{1}{\overline{g}_WP(g_M)}\right)
\bigg)
\bigg]
\frac{1}{\overline{g}_M}\exp\left(-\frac{g_M}{\overline{g}_M}\right) dg_M
\end{align*}
\end{multline}


Can someone please help? Thank in advance

• Welcome to TeX.SX. A tip: If you indent lines by 4 spaces, then they're marked as a code sample. You can also highlight the code and click the "code" button ({}) or select your code and hit Ctrl+K. Commented Mar 8, 2013 at 19:15
• I have edited your code to make it more legible. Why are you using multiline and align at the same time? It seems like you are missing alignment characters (ampersands &). Commented Mar 8, 2013 at 19:30

1 Answer

This is probably close enough to what you are trying to achieve:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
\begin{split}
C_s & = \max_{P(g_M)} \int_0^{\infty}
\bigg[ \left(1-\exp\left(-\frac{g_M}{\overline{g}_W}\right) \right)
\log\left(1+\frac{g_MP(g_M)}{N_M}\right) \\
&\quad -\int_0^{g_M} \log\left(1+\frac{g_WP(g_W)}{N_W}\right)
\frac{1}{\overline{g}_W}\exp\left(-\frac{g_W}{\overline{g}_W}\right)
dg_W \bigg]
\frac{1}{\overline{g}_W}\exp\left(-\frac{g_M}{\overline{g}_M}\right) dg_M
\end{split}\\
\begin{split}
& = \max_{P(g_M)} \int_0^{\infty}
\bigg[\log \left(1+\frac{g_MP(g_M)}{N_M}\right)
-\exp\left(\frac{1}{\overline{g}_WP(g_M)}\right)
\bigg(Ei\left(\frac{1}{\overline{g}_WP(g_M)}\right) \\
&\quad   -Ei\left(\frac{g_M}{\overline{g}_W}
+\frac{1}{\overline{g}_WP(g_M)}\right)
\bigg)
\bigg]
\frac{1}{\overline{g}_M}\exp\left(-\frac{g_M}{\overline{g}_M}\right) dg_M
\end{split}
\end{align*}

\end{document}


A couple of points:

• It is perfectly ok to use split inside align (see for instance this question).
• You should put the minus signs after line breaking.
• You don't need displaystyle as equations are already displayed in the align environment.
• You can improve the alignment by adding white space with \quad, \qquad or even \phantom.
• I wouldn't even use split, no need. Just ={}& and &- Commented Mar 8, 2013 at 19:52
• In this case you are right, there is no need to use split but the advantage I see in using it is that if we were using align then split would automatically take care of the tag, whereas otherwise you have to do it manually. Commented Mar 8, 2013 at 21:38