Here is the compiled result
and the code is here
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{setspace}
\begin{document}
\begin{equation}
\begin{aligned}
\det(\boldsymbol \omega(\pi_0), \pi) =
\left|
\frac{\partial(\boldsymbol \omega(\pi))}{\partial(\boldsymbol \omega(\pi_0))}
\right| & =
\left|
\frac{\partial(\boldsymbol \omega(\pi))}{\partial(\boldsymbol p(\pi))}
\frac{\partial(\boldsymbol p(\pi))}{\partial(\boldsymbol p(\pi_0))}
\frac{\partial(\boldsymbol p(\pi_0))}{\partial(\boldsymbol \omega(\pi_0))}
\right| \\
& =
\left|
\frac{\partial(\boldsymbol \omega(\pi))}{\partial(\boldsymbol p(\pi))}
\frac{\partial(\boldsymbol p(\pi))}{\partial(u, v)}
\frac{\partial(u, v)}{\partial(\boldsymbol p(\pi_0))}
\frac{\partial(\boldsymbol p(\pi_0))}{\partial(\boldsymbol \omega(\pi_0))}
\right| \\
& =
\frac{
\left|
\frac{\partial(\boldsymbol \omega(\pi))}{\partial(\boldsymbol p(\pi))}
\frac{\partial(\boldsymbol p(\pi))}{\partial(u, v)}
\right|
}{
\left|
\frac{\partial(\boldsymbol \omega(\pi_0))}{\partial(\boldsymbol p(\pi_0))}
\frac{\partial(\boldsymbol p(\pi_0))}{\partial(u, v)}
\right|
}
\end{aligned}
\label{equ_cpt3_6}
\end{equation}
\end{document}
The symbols in the last line appear smaller than those in the other lines. How can I make them appear in normal size?
