# Single equation number for a lengthy collection of equations

So I need to align a set of equations when one of the equations is very long. In addition, I need to number them only once and to be labeled (once). I think I succeeded in the alignment itself; however, the numbering keeps making me a problem, *,\notag and \nonumber are not helping, that's what I mean:

\begin{align}
\begin{split}\label{eq:26}
&-\kappa_0+\kappa_0\Gamma_{in2}= \frac{1+\Gamma_{in2}}{e^{j\kappa_1z_1}+\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}}\Big(\kappa_1\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}-\kappa_1e^{j\kappa_1z_1}\Big)
\end{split}\\
\begin{split}
\Big(&-\kappa_0+\kappa_0\Gamma_{in2}\Big)\Big(e^{j\kappa_1z_1}+\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}\Big)=\Big(1+\Gamma_{in2}\Big)\Big(\kappa_1\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}-\kappa_1e^{j\kappa_1z_1}\Big)
\end{split}\\
\begin{split}
\Gamma_{in2}\Big[\kappa_0e^{j\kappa_1z_1}+\kappa_0\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}-\kappa_1\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}+\kappa_1e^{-j\kappa_1z_1}\Big]=&\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}(\kappa_1+\kappa_0)\\
&+(\kappa_0-\kappa_1)e^{j\kappa_1z_1}\\
\end{split}\\
\begin{split}
\vdots
\end{split}\\
\begin{split}
&\Gamma_{in2}=\frac{\overrightarrow{\Gamma}_{12}e^{-j\kappa_1z_1}+\overrightarrow{\Gamma}_{01}e^{j\kappa_1z_1}}{\overrightarrow{\Gamma}_{12}\overrightarrow{\Gamma}_{01}e^{j\kappa_1z_1}+e^{-j\kappa_1z_1}}
\end{split}
\end{align}

That's my problem (\ref{eq:26})


Since you want to assign a single equation number to the full set of equations, I suggest you use an equation environment and, nested within it, an aligned environment. I further suggest you perform left-alignment of the four subequations. Two of the four subequations require a line break so that they can fit; I suggest you place the line breaks right before the associated = symbols.

Speaking for myself, I find the "look" of all those \overrightarrows to be quite heavy-handed and oppressive; \vec may do just as well.

\documentclass{article}
\usepackage{amsmath} % for 'aligned' env.

\begin{document}
\setcounter{equation}{25} % just for this example

\label{eq:26} \begin{aligned} % eq 1 &-\kappa_0+\kappa_0\Gamma_{\!\mathrm{in2}} = \frac{1+\Gamma_{\!\mathrm{in2}}}{e^{j\kappa_1z_1} +\vec{\Gamma}_{\!12}e^{-j\kappa_1z_1}} (\kappa_1\vec{\Gamma}_{\!12}e^{-j\kappa_1z_1}-\kappa_1e^{j\kappa_1z_1})\\[2ex] % eq 2 &(-\kappa_0+\kappa_0\Gamma_{\!\mathrm{in2}})(e^{j\kappa_1z_1} +\vec{\Gamma}_{\!12}e^{-j\kappa_1z_1})\\ &\quad =(1+\Gamma_{\!\mathrm{in2}})(\kappa_1\vec{\Gamma}_{\!12} e^{-j\kappa_1z_1} -\kappa_1e^{j\kappa_1z_1})\\[2ex] % eq 3 &\Gamma_{\!\mathrm{in2}}\bigl[\kappa_0e^{j\kappa_1z_1} +\kappa_0\vec{\Gamma}_{\!12}e^{-j\kappa_1z_1} -\kappa_1\vec{\Gamma}_{\!12}e^{-j\kappa_1z_1} +\kappa_1e^{-j\kappa_1z_1}\bigr] \\ &\quad =\vec{\Gamma}_{\!12}e^{-j\kappa_1z_1}(\kappa_1+\kappa_0) +(\kappa_0-\kappa_1)e^{j\kappa_1z_1}\\ &\vdots\\ % eq 4 &\Gamma_{\!\mathrm{in2}}=\frac{\vec{\Gamma}_{\!12}e^{-j\kappa_1z_1} +\vec{\Gamma}_{\!01}e^{j\kappa_1z_1}}{% \vec{\Gamma}_{\!12}\vec{\Gamma}_{\!01}e^{j\kappa_1z_1}+e^{-j\kappa_1z_1}} \end{aligned}
That's my problem \eqref{eq:26}.

\end{document}

• Thank you very much, I don't like \overrightarrow too, but in another set of the equations I need a left arrow, so to make it look similar I'm using these bulky arrows. Apr 21, 2020 at 12:17