# How to vertically center equation number in single long continued fraction?

Suppose I would like to get an equation number on the left into the middle of some long continued fraction like this Is there any simple way to do it?

MWE:

\documentclass{article}
\usepackage[cp1250]{inputenc}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}

\begin{document}

\begin{equation}
z(s)= z_1 +
\cfrac{1}{y_2+
\cfrac{1}{z_3+
\cfrac{1}{y_4+
\cfrac{1}{\ddots \raisebox{-2ex}{$+\cfrac{1}{z_{2n-3} + \cfrac{1}{y_{2n-2} + \cfrac{1}{z_{2n - 1} + \cfrac{1}{y_{2n}}}}}$}}}}}
\end{equation}

\end{document}

• To me it makes more sense if the equation number is vertically aligned with the = symbol and the main fraction line. – Matthias Nov 3 '17 at 23:45

Embed the formula in gathered:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\begin{gathered}
z(s)= z_1 +
\cfrac{1}{y_2+
\cfrac{1}{z_3+
\cfrac{1}{y_4+
\cfrac{1}{\ddots
\raisebox{-2ex}{$+\cfrac{1}{z_{2n-3} + \cfrac{1}{y_{2n-2} + \cfrac{1}{z_{2n - 1} + \cfrac{1}{y_{2n}}}}}$}}}}}
\end{gathered}
\end{equation}

\end{document} 