Well, you can use the usual fontsize commands like \small
or \footnotesize
to get a smaller font to print the equation. But in my eyes that looks ugly, I think better would be to name a term as extra variable to get the long line shorter and explain the new variable in an extra line.
However, in the following MWE I demonstrate the usage of \small
and \footnotesize
. Please see the leading {
and the closing }
to have the smaller font size only in the equation inside that {...}
:
\documentclass[a4paper,12pt]{article}
\usepackage{mathrsfs}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{revsymb4-1}% <==================================== REVSYMB4-1
\usepackage{latexsym}
\usepackage[a4paper, total={6in, 9in}]{geometry}
\usepackage{blindtext} % <==================== add dummy text to document
\begin{document}
\blindtext
\begin{eqnarray}\label{eq:longeq}
w &=& 100(\partial_x f)^3x^2
+\cot\theta \partial_x f \partial_x fx^2-\partial_x g x^2
+ \left(z^3-150zzz^2-20\epsilon f z^2\right)
\partial_x f \partial_x^2 f \nonumber\\
&& + \epsilon\left[ 200\left( xxx\cot\theta f^3
-1\right)(\partial_x g)^2
+\left( \cot\theta- yyy^3\right)\partial_x f
-\left(4-1000\cot\theta f^3
\right)g\partial_x^2 f \right]\partial_x g +20zzz^2+500f^2
\nonumber\\
&& +\left( \cdots \right).
\end{eqnarray}
{\small % <=============================================== lower fontsize
\begin{align}\label{eq:longequ} % <=====================================
w &= 100(\partial_x f)^3x^2
+\cot\theta \partial_x f \partial_x fx^2-\partial_x g x^2 \nonumber\\ % <========
&+ \left(z^3-150zzz^2-20\epsilon f z^2\right)
\partial_x f \partial_x^2 f \nonumber\\ % <=========================
&+ \epsilon\left[ 200\left( xxx\cot\theta f^3
-1\right)(\partial_x g)^2
+\left( \cot\theta- yyy^3\right)\partial_x f
-\left(4-1000\cot\theta f^3
\right)g\partial_x^2 f \right]\partial_x g \nonumber\\ % <==========
&+20zzz^2+500f^2 \nonumber\\ % <======================================
&+\left( \cdots \right).
\end{align}
} % <================================================= end lower fontsize
{\footnotesize % <======================================== lower fontsize
\begin{align}\label{eq:longequa} % <====================================
w &= 100(\partial_x f)^3x^2
+\cot\theta \partial_x f \partial_x fx^2-\partial_x g x^2 \nonumber\\
&+ \left(z^3-150zzz^2-20\epsilon f z^2\right)
\partial_x f \partial_x^2 f \nonumber\\
&+ \epsilon\left[ 200\left( xxx\cot\theta f^3
-1\right)(\partial_x g)^2
+\left( \cot\theta- yyy^3\right)\partial_x f
-\left(4-1000\cot\theta f^3
\right)g\partial_x^2 f \right]\partial_x g \nonumber\\
&+20zzz^2+500f^2 \nonumber\\
&+\left( \cdots \right).
\end{align}
} % <================================================= end lower fontsize
\blindtext
\end{document}
BTW I marked important code changings with <===========
. That is the resulting pdf:

Edit:
After the comment of user @barbarabeeton I tried the following MWE (added \blindtext
or free aditional text between the equations), but I can not recreate the behaviour described in the given link in the comment:
\documentclass[a4paper,12pt]{article}
\usepackage{mathrsfs}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{revsymb4-1}% <==================================== REVSYMB4-1
\usepackage{latexsym}
\usepackage[a4paper, total={6in, 9in}]{geometry}
\usepackage{blindtext} % <==================== add dummy text to document
\begin{document}
\blindtext
\begin{eqnarray}\label{eq:longeq}
w &=& 100(\partial_x f)^3x^2
+\cot\theta \partial_x f \partial_x fx^2-\partial_x g x^2
+ \left(z^3-150zzz^2-20\epsilon f z^2\right)
\partial_x f \partial_x^2 f \nonumber\\
&& + \epsilon\left[ 200\left( xxx\cot\theta f^3
-1\right)(\partial_x g)^2
+\left( \cot\theta- yyy^3\right)\partial_x f
-\left(4-1000\cot\theta f^3
\right)g\partial_x^2 f \right]\partial_x g +20zzz^2+500f^2
\nonumber\\
&& +\left( \cdots \right).
\end{eqnarray}
This is a short blindtext to test the behaviour of \verb|\small|.
This is a short blindtext to test the behaviour of \verb|\small|.
This is a short blindtext to test the behaviour of fontsize command. %\blindtext
{\small % <=============================================== lower fontsize
\begin{align}\label{eq:longequ} % <=====================================
w &= 100(\partial_x f)^3x^2
+\cot\theta \partial_x f \partial_x fx^2-\partial_x g x^2 \nonumber\\ % <========
&+ \left(z^3-150zzz^2-20\epsilon f z^2\right)
\partial_x f \partial_x^2 f \nonumber\\ % <=========================
&+ \epsilon\left[ 200\left( xxx\cot\theta f^3
-1\right)(\partial_x g)^2
+\left( \cot\theta- yyy^3\right)\partial_x f
-\left(4-1000\cot\theta f^3
\right)g\partial_x^2 f \right]\partial_x g \nonumber\\ % <==========
&+20zzz^2+500f^2 \nonumber\\ % <======================================
&+\left( \cdots \right).
\end{align}
} % <================================================= end lower fontsize
This is a short blindtext to test the behaviour of \verb|\small|.
This is a short blindtext to test the behaviour of \verb|\small|.
This is a short blindtext to test the behaviour of fontsize command.
{\footnotesize % <======================================== lower fontsize
\begin{align}\label{eq:longequa} % <====================================
w &= 100(\partial_x f)^3x^2
+\cot\theta \partial_x f \partial_x fx^2-\partial_x g x^2 \nonumber\\
&+ \left(z^3-150zzz^2-20\epsilon f z^2\right)
\partial_x f \partial_x^2 f \nonumber\\
&+ \epsilon\left[ 200\left( xxx\cot\theta f^3
-1\right)(\partial_x g)^2
+\left( \cot\theta- yyy^3\right)\partial_x f
-\left(4-1000\cot\theta f^3
\right)g\partial_x^2 f \right]\partial_x g \nonumber\\
&+20zzz^2+500f^2 \nonumber\\
&+\left( \cdots \right).
\end{align}
} % <================================================= end lower fontsize
\blindtext
\end{document}
with the result:

As you can see (marked with the two red arrows) there is no interaction with the line before {\small
or {\footnotesize
...
eqnarray
...amsmath
environments (align
,split
,multlines
)medsize
environment fromnccmath
, which is betweentextstyle
anddisplaystyle
(the latter is reduced by about 20%).eqnarray
, please help in this case if possible. Thank you so much.