How do you center equations?

Question

I can't seem to center equations without causing some weird formatting problem. The following results in the R being dropped:

\begin{center}
 E(R_{i,t})=E(\alpha_i)+E(\beta_{i,F_1 } F_{1,t})+E(\beta_{i,F_2 } F_{2,t})+\ldots+E(\beta_{i,F_m } F_{m,t})\linebreak
\bar{R}_{i,t}=a+\hat{\beta}_{i,F_1 } E(F_{1,t})+\hat{\beta}_{i,F_2 } E(F_{2,t})+\ldots+\hat{\beta}_{i,F_m } E(F_{m,t})\linebreak
\bar{R}_{i,t}=a+\gamma_1\hat{\beta}_{i,F_1 } +\gamma_2\hat{\beta}_{i,F_2 } F_{2,t}+\ldots+\gamma_m\hat{\beta}_{i,F_m }
\end{center}

Any ideas? Is {center} the wrong thing to use?

Answer 1

For a series of centered equations use the gather environment of amsmath:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{gather*}
 E(R_{i,t})=E(\alpha_i)+E(\beta_{i,F_1 } F_{1,t})+E(\beta_{i,F_2 } F_{2,t})+
    \ldots+E(\beta_{i,F_m } F_{m,t})\\
\bar{R}_{i,t}=a+\hat{\beta}_{i,F_1 } E(F_{1,t})+\hat{\beta}_{i,F_2 } E(F_{2,t})+
    \ldots+\hat{\beta}_{i,F_m } E(F_{m,t})\\
 \bar{R}_{i,t}=a+\gamma_1\hat{\beta}_{i,F_1 } +\gamma_2\hat{\beta}_{i,F_2 } F_{2,t}+
    \ldots+\gamma_m\hat{\beta}_{i,F_m }
\end{gather*} 
\end{document}

Instead of centering you may consider to align all equations at the equal sign and center the whole multiline environment. For this, use the align or align* environment, see the amsmath user's guide (or type texdoc amsldoc at the command prompt).

In any case, use amsmath. That package provides many kinds of multiline diplayed formula environments.

Answer 2

The center environment is for text, not math. What you want here is (this also lines up the equals signs):

\begin{align*}
  E(R_{i,t})    &= E(\alpha_i)+E(\beta_{i,F_1 } F_{1,t})+E(\beta_{i,F_2 } F_{2,t})+\ldots+E(\beta_{i,F_m } F_{m,t}) \\
  \bar{R}_{i,t} &= a+\hat{\beta}_{i,F_1 } E(F_{1,t})+\hat{\beta}_{i,F_2 } E(F_{2,t})+\ldots+\hat{\beta}_{i,F_m } E(F_{m,t}) \\
  \bar{R}_{i,t} &= a+\gamma_1\hat{\beta}_{i,F_1 } +\gamma_2\hat{\beta}_{i,F_2 } F_{2,t}+\ldots+\gamma_m\hat{\beta}_{i,F_m }
\end{align*}

You need the amsmath package for align*, so make sure you have the line \usepackage{amsmath} in your preamble (before \begin{document}).