equations
I am trying to have a multiline equation without any numbering, even not in the last one.
\begin{align}
a = x \nonumber \\
b = y
\end{align}
However, this is producing a line number in the last line, which would like not to happen.
I have also tried the equation and equation* environments with no luck.
Thanks.
P.S. What' the markup for rendering LaTeX code. Can't seem to be able to find it in the help page?
I would definitely go the second way with $\displaystyle: I find that it looks strange to have something centered after a bullet. To get the vertical alignment correct, just add [t] after \begin{aligned}, where "t" means "top". (See also the top of page 8 of the User's guide for the amsmath Package.)
As far as understand question, you looking for something like this:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{multline}
W = \int_{k<\Lambda} [Dg][DA][D\psi][D\Phi] \exp\biggl\{ i \int d^{4}x \sqrt{-g} \biggl[\frac{m_{p}^{2}}{2}R- \frac{1}{4}F_{\mu\nu}^{a}F^{a\mu\nu}\\
%
\qquad + i\bar{\psi}^i\gamma^{\mu}D_{\mu}\psi^i + \bigl(\bar{\psi}_{L}^{i} V_{ij} \Phi \psi_{R}^{j} + h.c. \bigr) - |D_{\mu}\Phi|^2 - V(\Phi)\biggr] \biggr\}
\end{multline}
\end{document}
Reason, why you receive errors in your effort to split equations, is use \left ... \right parenthesis, as explained @Przemysław Scherwentke in his answer.
Edit: As suggested @egreg, with \bigg size of parenthesis the equation looks nicer.
Edit (2): To vertical centering of equation number can be obtain width mathtolls package environment `multilined:
\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{equation}
\begin{multlined}
W = \int_{k<\Lambda} [Dg][DA][D\psi][D\Phi] \exp\biggl\{i \int d^{4}x \sqrt{-g} \biggl[\frac{m_{p}^{2}}{2}R- \frac{1}{4}F_{\mu\nu}^{a}F^{a\mu\nu} \\
%
\qquad + i\bar{\psi}^i\gamma^{\mu}D_{\mu}\psi^i + \bigl(\bar{\psi}_{L}^{i} V_{ij} \Phi \psi_{R}^{j} + h.c. \Bigr) - |D_{\mu}\Phi|^2 - V(\Phi)\biggr] \biggr\}
\end{multlined}
\end{equation}
\end{document}
which gives:
Best Answer
How about:
If you do use the unstarred version, remember that
\nonumberoperates on only one line, so to omit numbers entirely,\nonumber(or\notag) must be input for every line.