[Tex/LaTex] Rescaling equation in align+split environment – Numbering problem

alignnumberingsplit

I'm trying to rescale my to long equation in align + split environment (to get only one numbering). I found a method from here which is pretty useful.

However, the numbering is altered and is indicated below the equations instead of at the right. I guess it's due to the \parbox command but I don't know how to fix it.

Here is a MWE, with a long equation:

enter image description here

\documentclass{article}

\usepackage{graphicx}
\usepackage{amsmath}

\begin{document}
\scalebox{0.8}{\parbox{.5\linewidth}{%
\begin{align}
\begin{split}
C_{M,i}(x) = &-\frac{e^{\text{Ha}_{i} - x \, \frac{k}{D_{\text{NO},t}}}\left(\left(-1 + e^{\text{H\~{a}}_{i}}\right)\left(-1+\text{Mu}_{i}+e^{\text{H\~{a}}_{i}}(1+\text{Mu}_{i})\right) \, Pr + 2 \, e^{\text{H\~{a}}_{i}} \, k \, \lambda_{\text{air},i} \, C_{i}(t,z) \right)}{2 \, k \left(-1 + \text{Mu}_{i} + e^{2 \, (\text{Ha}_{i}+\text{H\~{a}}_{i})}(1+\text{Mu}_{i})\right)} \\
&+\frac{e^{\text{Ha}_{i} + x \, \frac{k}{D_{\text{NO},t}}}\left(\left(-1+e^{\text{H\~{a}}_{i}}\right)\left(-1+\text{Mu}_{i} + e^{\text{H\~{a}}_{i}}(1+\text{Mu}_{i})\right) \, Pr + 2 \, e^{\text{H\~{a}}_{i}} \, k \, \lambda_{\text{air},i} \, C_{i}(t,z)\right)}{2 \, k \, \left(-1+\text{Mu}_{i} + e^{2(\text{Ha}_{i} + \text{H\~{a}}_{i})}(1+\text{Mu}_{i})\right)}
\end{split}
\end{align}
}}
\end{document}

Best Answer

If you really want to scale the equations, do it properly:

\documentclass{article}
\usepackage{amsmath,graphicx}

\begin{document}

\begin{equation}
\resizebox{.8\textwidth}{!}{%
  $\begin{aligned}
   C_{M,i}(x) ={}
   & -\frac{
        e^{\mathrm{Ha}_{i} - x \frac{k}{D_{\mathrm{NO},t}}}
        \bigl(
          (-1 + e^{\mathrm{H\tilde{a}}_{i}})(-1+\mathrm{Mu}_{i} +
            e^{\mathrm{H\tilde{a}}_{i}}(1+\mathrm{Mu}_{i}))Pr +
          2e^{\mathrm{H\tilde{a}}_{i}} k\lambda_{\mathrm{air},i}  C_{i}(t,z)
        \bigr)
      }{
        2k(-1 + \mathrm{Mu}_{i} + e^{2(\mathrm{Ha}_{i}+\mathrm{H\tilde{a}}_{i})}(1+\mathrm{Mu}_{i}))
      }
   \\
   & +\frac{
        e^{\mathrm{Ha}_{i} + x \frac{k}{D_{\mathrm{NO},t}}}
        \bigl(
          (-1+e^{\mathrm{H\tilde{a}}_{i}})(-1+\mathrm{Mu}_{i} +
           e^{\mathrm{H\tilde{a}}_{i}}(1+\mathrm{Mu}_{i}))Pr +
          2e^{\mathrm{H\tilde{a}}_{i}}  k\lambda_{\mathrm{air},i}  C_{i}(t,z))
      }{
        2k(-1+\mathrm{Mu}_{i} + e^{2(\mathrm{Ha}_{i} + \mathrm{H\tilde{a}}_{i})}(1+\mathrm{Mu}_{i}))
     }
  \end{aligned}$%
}
\end{equation}

\end{document}

enter image description here

I removed all \left and \right; also all \, commands (they were wrong). I only used \bigl( and \bigr) in the outermost parentheses of the big expressions.

Don't use \text, but \mathrm in this context.