LaTex equation out of page margin

Question

I am a LaTex beginner and I am writing my first formal document using it.
I have to write a quite long equation, and it goes out of page bounds for some reason as I show here:

Here you are the code I run:

\begin{align}
\begin{split}
f(x,y,z,w) = (x+y+z+\bar{w}) * (x+y+\bar{z}+\bar{w}) * (x+\bar{y}+z+w) * (x+\bar{y}+\bar{z}+w) * (x+\bar{y}+\bar{z}+\bar{w}) * (\bar{x}+y+z+w) * (\bar{x}+y+z+\bar{w}) * (\bar{x}+y+\bar{z}+w) * (\bar{x}+\bar{y}+z+\bar{w}) * (\bar{x}+\bar{y}+\bar{z}+w) 
\end{split}
\end{align}

How can I solve this? Thank you for your patience and consideration.

Answer 1

One possible solution....to split it....with edit by comment of the user.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\begin{document}
\begin{align}
\begin{split}
f(x,y,z,w) & = (x+y+z+\bar{w})\cdot (x+y+\bar{z}+\bar{w})\cdot (x+\bar{y}+z+w) \\
&\cdot  (x+\bar{y}+\bar{z}+w) \cdot (x+\bar{y}+\bar{z}+\bar{w}) \cdot (\bar{x}+y+z+w) \\
&\cdot (\bar{x}+y+z+\bar{w}) \cdot (\bar{x}+y+\bar{z}+w)\\
& \cdot (\bar{x}+\bar{y}+z+\bar{w}) \cdot  (\bar{x}+\bar{y}+\bar{z}+w)
\end{split}
\end{align}
\end{document}

Answer 2

I can propose an autosplit environment, but it's much better to split the big thing by hand as in the last example.

The optional argument to autosplit is the fraction of the display width to fill. The default is 0.9 (that is, 90%).

\documentclass{article}
\usepackage{amsmath}

\newenvironment{autosplit}[2][0.9]
 {%
  \settowidth{\dimen0}{$#2{}$}%
  \begin{tabular}{@{}c@{}}
  $\displaystyle#2{}$%
  \begin{minipage}[t]{\dimexpr#1\displaywidth-\dimen0}
  %\raggedright
  $\displaystyle
 }
 {$\end{minipage}\end{tabular}}

\begin{document}

\begin{equation}
\begin{autosplit}{f(x,y,z,w) =}
  (x+y+z+\bar{w}) \* (x+y+\bar{z}+\bar{w}) \* (x+\bar{y}+z+w) \* 
  (x+\bar{y}+\bar{z}+w) \* (x+\bar{y}+\bar{z}+\bar{w}) \* (\bar{x}+y+z+w) \* 
  (\bar{x}+y+z+\bar{w}) \* (\bar{x}+y+\bar{z}+w) \* (\bar{x}+\bar{y}+z+\bar{w}) \* 
  (\bar{x}+\bar{y}+\bar{z}+w) 
\end{autosplit}
\end{equation}

\begin{equation}
\begin{autosplit}[0.8]{f(x,y,z,w) =}
  (x+y+z+\bar{w}) \* (x+y+\bar{z}+\bar{w}) \* (x+\bar{y}+z+w) \* 
  (x+\bar{y}+\bar{z}+w) \* (x+\bar{y}+\bar{z}+\bar{w}) \* (\bar{x}+y+z+w) \* 
  (\bar{x}+y+z+\bar{w}) \* (\bar{x}+y+\bar{z}+w) \* (\bar{x}+\bar{y}+z+\bar{w}) \* 
  (\bar{x}+\bar{y}+\bar{z}+w) 
\end{autosplit}
\end{equation}

\begin{equation}
\begin{split}
f(x,y,z,w)={}&
  (x+y+z+\bar{w}) (x+y+\bar{z}+\bar{w}) (x+\bar{y}+z+w) \\
{}\cdot{}&
  (x+\bar{y}+\bar{z}+w) (x+\bar{y}+\bar{z}+\bar{w}) (\bar{x}+y+z+w) \\
{}\cdot{}&
  (\bar{x}+y+z+\bar{w}) (\bar{x}+y+\bar{z}+w) (\bar{x}+\bar{y}+z+\bar{w}) \\
{}\cdot{}&
  (\bar{x}+\bar{y}+\bar{z}+w) 
\end{split}
\end{equation}

\end{document}