I'd like to suggest something that doesn't require extra packages.
Break your document into separate files for each of the sections. Make sure that one of these files is the section you want to show / hide; let's call it eigenDecomp.tex, and assume it follows the main section of the document. You can include those files in linear_algebra.tex, using \include{}. Then, you use the \includeonly{} command in the preamble to include only the sections you need.
So, building on the example I gave here for a similar question, you'd do something like this:
\documentclass{report}
\begin{document}
\include{introduction}
\include{main}
\include{eigenDecomp}
\include{conclusions}
\end{document}
Then, when you only want to include a few sections, you do this:
\documentclass{report}
\includeonly{introduction,main,conclusions}
\begin{document}
Note that the only drawback of this is that you can't nest \include{} commands, so you might have quite a complex file structure in linear_algebra.tex.
There are also other options you could consider such as the package Comment that allow you to selectively hide or reveal text based on labels.