Several equations and align environments have additional newlines before and/or after them.
If one makes the following substitutions to comment out those newlines: \n\n\begin{equation} -> \n%\n\begin{equation}, \end{equation}\n\n -> \end{equation}%\n\n (and similarly for align and alignat) -- commenting out the newlines prevents additional whitespace but keeps the source readable -- then the whitespace is reduced significantly:

On making these changes, the book becomes 384 pages long instead of 388 pages.
Also, there is a \usepackage{booktabs} in the preamble but the tables drawn do not follow the booktabs manual; lots of horizontal and vertical lines are used. Here's what a table edited according to the booktabs style looks like compared to one of the current tables:

I will submit a PR if you like the suggested changes.
Several equations and align environments have additional newlines before and/or after them.
If one makes the following substitutions to comment out those newlines:
\n\n\begin{equation}->\n%\n\begin{equation},\end{equation}\n\n->\end{equation}%\n\n(and similarly for align and alignat) -- commenting out the newlines prevents additional whitespace but keeps the source readable -- then the whitespace is reduced significantly:On making these changes, the book becomes 384 pages long instead of 388 pages.
Also, there is a
\usepackage{booktabs}in the preamble but the tables drawn do not follow thebooktabsmanual; lots of horizontal and vertical lines are used. Here's what a table edited according to thebooktabsstyle looks like compared to one of the current tables:I will submit a PR if you like the suggested changes.