In addition to recommending that you use the align
environment (provided by the amsmath
package) instead of the eqnarray*
environment, I would also suggest you make each line's first +
symbol the alignment point, rather than the =
symbol; that way, the structure of the equation should become very readily apparent. And, since the string \bigg|_{z = z_{0}}
occurs no fewer than six times, it's handy to create a shortcut macro for it.
\documentclass{article}
\usepackage{amsmath} % provides the "align" environment
\newcommand\atz{\bigg\vert_{z=z_0}\!} % a shortcut macro
\begin{document}
\begin{align}
f_{\textit{lin}}(z) = f(z_{0})
&+
\frac{\partial f(z)}{\partial \ddot{\theta}}\atz \ddot{\theta} +
\frac{\partial f(z)}{\partial \ddot{\alpha}}\atz \ddot{\alpha} +
\frac{\partial f(z)}{\partial \dot{\theta}}\atz \dot{\theta} \notag \\
&+ \frac{\partial f(z)}{\partial \dot{\alpha}}\atz \dot{\alpha} +
\frac{\partial f(z)}{\partial \theta}\atz \theta +
\frac{\partial f(z)}{\partial \alpha}\atz \alpha
\end{align}
\end{document}
If you don't want to use the align
environment, you could use a split
environment inside an equation
environment; the main difference is that there's a single equation number that's centered vertically across the rows of the equation
:
\documentclass{article}
\usepackage{amsmath}
\newcommand\atz{\bigg\vert_{z=z_0}\!} % a shortcut macro
\begin{document}
\begin{equation}
\begin{split}
f_{\textit{lin}}(z) = f(z_{0})
&+
\frac{\partial f(z)}{\partial \ddot{\theta}}\atz \ddot{\theta} +
\frac{\partial f(z)}{\partial \ddot{\alpha}}\atz \ddot{\alpha} +
\frac{\partial f(z)}{\partial \dot{\theta}}\atz \dot{\theta} \\[1ex] % some additional vertical separation
&+ \frac{\partial f(z)}{\partial \dot{\alpha}}\atz \dot{\alpha} +
\frac{\partial f(z)}{\partial \theta}\atz \theta +
\frac{\partial f(z)}{\partial \alpha}\atz \alpha
\end{split}
\end{equation}
\end{document}
*
form means don't number useeqnarray
to get a number (but better to usealign
)