Putting one line of an align environment in a different font size

Question

I have to format a .tex file following certain guidelines. I have an equation which has one line which is very big, and the only way I see of making it fit into the page (other than substantial rewriting or really messy notation) is to put it in a smaller font size. The rest of the equation is fine, so I would like to keep that in normal size, if possible. Thus, I would like to do something like:

\begin{align*}
line 1\\
line 2\\
{\small huge line}\\
line 4
\end{align*}

Is this possible? And what is the correct way to do it?

Answer 1

I would use the medium size commands from nccmath : \medmath, \medop, \medint, \mfrac, &c., which reduces the size to about 80 % of \displaystyle:

\begin{align*}
line 1\\
line 2\\
\medmath{huge line}\\
line 4
\end{align*}

Note \medmath cannot include the alignment markers&.

However, the result will usually be nicer if you break the longer lines with one of the split, aligned or multlined environments.