Equation Numbering – How to Assign Equation Number to Last Equation and Align Right

equationsnumbering

\begin{align*}
\epsilon_x (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_x(i, j, k)\varphi(i + 1, j, k) + \\
\epsilon_y (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_y(i, j, k)\varphi(i + 1, j, k) +  \\
\epsilon_z (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_z(i, j, k)\varphi(i + 1, j, k) -  \\
(\epsilon_x(i - 1, j, k) + \epsilon_x(i, j, k) + \epsilon_y(i, j - 1,k) + \epsilon_y(i, j, k) \\
  + \epsilon_z(i, j, k - 1) + \epsilon_z(i, j, k))\varphi(i, j, k) + \\
  h^2\lambda(i, j, k) k^2 \varphi(i, j, k) = - \frac{4\pi\rho(i, j, k)}{h} \label{eq:2}
\end{align*}

How to assign equation number to the last equation only and align it to the right?

result

Best Answer

Here is a solution using the IEEEeqnarray* environment from the IEEEtrantools package. This environment provides a tabular like syntax and it is possible to achieve most types of alignment using this environment.

The * version of the environment is used for equations without numbering. To insert an equation number in such an environment, \IEEEyesnumber command can be used.

enter image description here

\documentclass{article}

\usepackage{amsmath}
\usepackage{IEEEtrantools}

\begin{document}
\begin{IEEEeqnarray*}{rCl}
    \IEEEeqnarraymulticol{3}{l}{\epsilon_x (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_x(i, j, k)\varphi(i + 1, j, k) +{}} \\
    \IEEEeqnarraymulticol{3}{l}{\epsilon_y (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_y(i, j, k)\varphi(i + 1, j, k) +{}} \\
    \IEEEeqnarraymulticol{3}{l}{\epsilon_z (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_z(i, j, k)\varphi(i + 1, j, k) -{}} \\
    \IEEEeqnarraymulticol{3}{l}{(\epsilon_x(i - 1, j, k) + \epsilon_x(i, j, k) + \epsilon_y(i, j - 1,k) + \epsilon_y(i, j, k) } \\
    \IEEEeqnarraymulticol{3}{l}{ {} + \epsilon_z(i, j, k - 1) + \epsilon_z(i, j, k))\varphi(i, j, k) + } \\
    h^2\lambda(i, j, k) k^2 \varphi(i, j, k) &=& - \frac{4\pi\rho(i, j, k)}{h} \IEEEyesnumber\label{eq:2}
\end{IEEEeqnarray*}
\end{document}

Edit: I missed the part of your question about right alignment. Do you want something like this?

enter image description here

This can be achieved using only one right-aligned column.

\documentclass{article}

\usepackage{amsmath}
\usepackage{IEEEtrantools}

\begin{document}
\begin{IEEEeqnarray*}{r}
    \epsilon_x (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_x(i, j, k)\varphi(i + 1, j, k) +{} \\
    \epsilon_y (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_y(i, j, k)\varphi(i + 1, j, k) +{} \\
    \epsilon_z (i - 1, j, k) \varphi (i -1, j, k) + \epsilon_z(i, j, k)\varphi(i + 1, j, k) -{} \\
    (\epsilon_x(i - 1, j, k) + \epsilon_x(i, j, k) + \epsilon_y(i, j - 1,k) + \epsilon_y(i, j, k) \\
    {} + \epsilon_z(i, j, k - 1) + \epsilon_z(i, j, k))\varphi(i, j, k) + \\
      h^2\lambda(i, j, k) k^2 \varphi(i, j, k) = - \frac{4\pi\rho(i, j, k)}{h} \IEEEyesnumber\label{eq:2}
\end{IEEEeqnarray*}
\end{document}
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