# Multiple align points and multiple equations

I have 2 equations, both have to be numbered and aligned. Equations' numbers should be vertically centered. But equations are long and have to be broken into 2 or 3 lines each. It would be great to have 2 alignment points in each line. But I cannot achieve that using split. Or can I? Here is the MWE:

\begin{align}
\begin{split}
z_1^{i,j}
& = a_1 \, x_1^{i,j} + b_1 \, \delta_1^{i,j} \\
& + \sum_k y_k^{i,j} \qquad \forall ~i,j
\end{split}
\\
\begin{split}
z_2^{i,j}
& = a_2 \, x_2^{i,j} + b_2 \, \delta_2^{i,j} + c_2 \\
& + z_1^{i,j} \qquad \forall ~i,j
\end{split}
\end{align}


Basically, I want the same output as produced with this code, especially equations' numbers vertically centered. In addition, I want \forall ~i,j from both equations to be also aligned, i.e. below each other. Solution with alignat instead align would be even better for me.

I believe you're using a two column format.

The environment split only accepts one alignment point; you can use \mathmakebox from mathtools (that also loads amsmath) and calc:

\documentclass[twocolumn]{article}
\usepackage{mathtools}
\usepackage{calc}

\begin{document}
\begin{align}
\begin{split}
z_1^{i,j}
& = a_1^{} x_1^{i,j} + b_1^{} \delta_1^{i,j} \\
\end{split}
\\
\begin{split}
z_2^{i,j}
& = a_2^{} x_2^{i,j} + b_2^{} \delta_2^{i,j} + c_2^{} \\
& \qquad + \mathmakebox[\widthof{$\displaystyle\sum_k y_k^{i,j}$}][l]{z_1^{i,j}}
\end{split}
\end{align}
\end{document}


Note that \, between factors is not used, while ^{} is recommended in order to push subscripts at the same level. The + on the second line shouldn't be under the equals sign, as it belongs to the right hand side of the expression.

However, the subscripts are not really level, because of j at the exponent, so you might want a slightly more complex adjustment:

\documentclass[twocolumn]{article}
\usepackage{mathtools}
\usepackage{calc}

\begin{document}
\begin{align}
\begin{split}
z_1^{i,j}
\end{split}
\\
\begin{split}
z_2^{i,j}
& \qquad + \mathmakebox[\widthof{$\displaystyle\sum_k y_k^{i,j}$}][l]{z_1^{i,j}}
\end{split}
\end{align}
\end{document}


• Works nice. It's very elegant solution and just what I wanted. And the \adjs command is just beautiful. – MMSt Sep 19 '14 at 8:48

Well there is no problem with each of your equations in one line, and the ∀ symbols can be aligned with the alignat environment:

\documentclass[12pt]{article}

\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage[showframe]{geometry}

\begin{document}

\begin{alignat}{2}
z_1^{i,j}    & = a_1 \, x_1^{i,j} + b_1 \, δ_1^{i,j}
+ ∑_k y_k^{i,j} &  \qquad &  ∀ ~i,j \\
z_2^{i,j}
& = a_2 \, x_2^{i,j} + b_2 \, δ_2^{i,j} + c_2
+ z_1^{i,j}  &  &  ∀ ~i,j
\end{alignat}

\end{document}