How to reduce the equation font size in math mode in Latex?

Question

I am trying to resize the equation font size in math mode:

As This answer suggested :

\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx}
\newcommand*{\Scale}[2][4]{\scalebox{#1}{$#2$}}%
\newcommand*{\Resize}[2]{\resizebox{#1}{!}{$#2$}}%
\begin{document}
\[y = \sin^2 x\]
%
\[\Scale[0.5]{y = \sin^2 x}\]
%
\[ \Resize{1cm}{y = \sin^2 x}\]
\end{document}

Where my equation look like this:

\begin{equation}
\begin{aligned}
\mathbf{H_{2}^{(l+1)}=\sigma(\alpha_{22}^{(l)} H_{2}^{(l)} W^{(l)}+\alpha_{21}^{(l)} H_{1}^{(l)} W^{(l)}  \\
 +\alpha_{23}^{(l)} H_{3}^{(l)} W^{(l)}+\alpha_{24}^{(l)} H_{4}^{(l)} W^{(l)} )}
 \end{aligned}
\end{equation}

it's going outside of paper width.

How to reduce the font or use this code to reduce font of equation inside paper width?

Thank you !

Answer 1

Instead of shrinking the font size, it is generally better to use a line break. For that purpose the amsmath package provides the multline environment. From the documentation:

The multline environment is a variation of the equation environment used for equations that don't fit on a single line. The first line of a multline will be at the left margin and the last line at the right margin, except for an indention on both sides in the amount of \multlinegap. Any additional lines in between will be centered independently within the display width (unless the fleqn option is in effect).

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\usepackage{blindtext}
\begin{document}
\blindtext
\begin{multline}
    H_{2}^{(l+1)}
    = \sigma ( \alpha_{22}^{(l)} H_{2}^{(l)} W^{(l)} + \alpha_{21}^{(l)} H_{1}^{(l)} W^{(l)}  \\
    + \alpha_{23}^{(l)} H_{3}^{(l)} W^{(l)} + \alpha_{24}^{(l)} H_{4}^{(l)} W^{(l)} )
\end{multline}
\Blindtext
\end{document}