Turning off marginpar (marginparwidth) while in multicols environment - latex

Question

I'm trying to turn off marginpar when starting a new multicols environment with this:
\renewenvironment{multicols}[1]{%
\let\oldmarginparwidth\marginparwidth
\setlength{\marginparwidth}{0}%
\begin{multicols}{#1}
}{%
\end{multicols}%
\setlength{\marginparwidth}{\oldmarginparwidth}%
}
However, it doesn't work. What am I missing?

Answer 1

The command you've got there won't work mid-page, you need to use the changepage package to do that.
\usepackage{changepage}
I take it you're trying to take up the full width of the page. I nicked this from the tufte-latex class:
First, define an 'overhang' amount that'll be added to the textwidth at the beginning and subtracted at the end:
\newlength{\overhang}
\setlength{\overhang}{\marginparwidth}
\addtolength{\overhang}{\marginparsep}
Then use \adjustwidth with the overhang amount when you want to remove marginpar space:
\begin{adjustwidth}{}{-\overhang}
% This will be displayed full-width
\end{adjustwidth}{}{-\overhang}
As Damien pointed out, you can still use marginpars like this, they'll just exceed the pagewidth. \multicols will prevent you from using floats, however.
Hope that's what you need!

Answer 2

I'm not sure exactly what you're looking for here, but generally marginpars aren't allowed in multicols already. From the multicol documentation:
...floats and marginpars are not allowed in the current implementation [This is dictated by lack of time. To implement floats one has to reimplement the whole LATEX output routine.].

Answer 3

I have managed to get it working by using the chngpage package and defining a new environment which sets/resets different values before/after that environment.
However, I still have a problem on the last page of each \chapter: header width on the last page of the chapter