Single equation number for a lengthy collection of equations

Question

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_0Gamma_{in2}= frac{1+Gamma_{in2}}{e^{jkappa_1z_1}+overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}}Big(kappa_1overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}-kappa_1e^{jkappa_1z_1}Big)
end{split}
begin{split}
 Big(&-kappa_0+kappa_0Gamma_{in2}Big)Big(e^{jkappa_1z_1}+overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}Big)=Big(1+Gamma_{in2}Big)Big(kappa_1overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}-kappa_1e^{jkappa_1z_1}Big)
end{split}
begin{split}
Gamma_{in2}Big[kappa_0e^{jkappa_1z_1}+kappa_0overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}-kappa_1overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}+kappa_1e^{-jkappa_1z_1}Big]=&overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}(kappa_1+kappa_0)
 &+(kappa_0-kappa_1)e^{jkappa_1z_1}
end{split}
begin{split}
vdots
end{split}
begin{split}
&Gamma_{in2}=frac{overrightarrow{Gamma}_{12}e^{-jkappa_1z_1}+overrightarrow{Gamma}_{01}e^{jkappa_1z_1}}{overrightarrow{Gamma}_{12}overrightarrow{Gamma}_{01}e^{jkappa_1z_1}+e^{-jkappa_1z_1}}
end{split}
end{align}

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

Thanks in advance.

Mico · Answer

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

begin{equation}label{eq:26}
begin{aligned}
% eq 1
&-kappa_0+kappa_0Gamma_{!mathrm{in2}}
  = frac{1+Gamma_{!mathrm{in2}}}{e^{jkappa_1z_1}
    +vec{Gamma}_{!12}e^{-jkappa_1z_1}}
  (kappa_1vec{Gamma}_{!12}e^{-jkappa_1z_1}-kappa_1e^{jkappa_1z_1})[2ex]
% eq 2
&(-kappa_0+kappa_0Gamma_{!mathrm{in2}})(e^{jkappa_1z_1}
  +vec{Gamma}_{!12}e^{-jkappa_1z_1})
&quad =(1+Gamma_{!mathrm{in2}})(kappa_1vec{Gamma}_{!12} 
  e^{-jkappa_1z_1} -kappa_1e^{jkappa_1z_1})[2ex]
% eq 3
&Gamma_{!mathrm{in2}}bigl[kappa_0e^{jkappa_1z_1}
  +kappa_0vec{Gamma}_{!12}e^{-jkappa_1z_1}
  -kappa_1vec{Gamma}_{!12}e^{-jkappa_1z_1}
  +kappa_1e^{-jkappa_1z_1}bigr] 
&quad =vec{Gamma}_{!12}e^{-jkappa_1z_1}(kappa_1+kappa_0) 
  +(kappa_0-kappa_1)e^{jkappa_1z_1}
&vdots
% eq 4
&Gamma_{!mathrm{in2}}=frac{vec{Gamma}_{!12}e^{-jkappa_1z_1}
  +vec{Gamma}_{!01}e^{jkappa_1z_1}}{%
   vec{Gamma}_{!12}vec{Gamma}_{!01}e^{jkappa_1z_1}+e^{-jkappa_1z_1}}
end{aligned}
end{equation}
That's my problem eqref{eq:26}.

end{document}

Single equation number for a lengthy collection of equations

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