Alignment of multiple align-blocks

Question

I try to align multiple blocks of equations in such a way that the same alignment is used for the different blocks. I am currently using align with an array-environment for each line. By specifying the width of the columns, I can ensure the correct alignment. However, the equation number is now not correctly aligned. I prefer the alignment of the second attempt in the example below, but then with the vertical alignment of the equation number of the first attempt.

\section{attempt 1}
\begin{align}
    &\text{s.t.} &\quad& \sum\limits_{i \in I_{j}^2} x_i \geq 1, &\qquad\qquad&  \forall j \in J \label{myLabel}\\
    &\text{s.t.} && \sum\limits_{i \in I_{j}^2} x_i \geq 1, &&  \forall j \in J
\end{align}

\text{Here is some text and possibly a new section}

\subsection{new subsection}

\begin{align}
    &\text{s.t.} &\quad& \sum\limits_{i \in I_{j}^2} x_i + y_i + z_i\geq 1, &\qquad\qquad&  \forall j \in J \label{myLabel}\\
    &\text{s.t.} && \sum\limits_{i \in I_{j}^2} x_i \geq 1, &&  \forall j \in J
\end{align}

\section{attempt 2}
\begin{align}
 \begin{array}{p{0.8 cm} p{6.2 cm} p{2 cm}}
s.t. & $\sum\limits_{i \in I_{j}^2} x_i \geq 1,$    & $ \forall j \in J$
\end{array}\\
\begin{array}{p{0.8 cm} p{6.2 cm} p{2 cm}}
s.t. & $\sum\limits_{i \in I_{j}^2} x_i \geq 1,$    & $ \forall j \in J$
\end{array}
\end{align}

\text{Here is some text and possibly a new section}

\subsection{new subsection}

\begin{align}
 \begin{array}{p{0.8 cm} p{6.2 cm} p{2 cm}}
s.t. & $\sum\limits_{i \in I_{j}^2} x_i \geq 1,$    & $ \forall j \in J$
\end{array}\\
\begin{array}{p{0.8 cm} p{6.2 cm} p{2 cm}}
s.t. & $\sum\limits_{i \in I_{j}^2} x_i + y_j \geq 1,$  & $ \forall j \in J$
\end{array}
\end{align}

Is there a way to do this? Either by fixing the width of columns in align or by changing the vertical alignment of equation numbers in array.

Answer 1

You can have more alignment points in the same align or you use an alignat environment.

But here is what you have asked for (in case I got you right):

% arara: latex

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\begin{align}
    \begin{array}{p{0.8 cm} p{6.2 cm} p{3.2 cm}} % reduced the width in order to fit on the line
        s.t. & $\sum\limits_{i \in I_{j}^2} x_i \geq 1,$    & $ \forall j \in J$
    \end{array}\label{myLabel} % removed back slashes here
\end{align}
\end{document}

You can see that the number on the right appears to be a bit too low. This is due to the limits of your sum operator.

If you use the typical approach instead, this will be just fine:

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\begin{alignat}{3}
    &\text{s.t.} &\quad& \sum\limits_{i \in I_{j}^2} x_i \geq 1, &\qquad\qquad&  \forall j \in J \label{myLabel}\\
    &\text{s.t.} && \sum\limits_{i \in I_{j}^2} x_i \geq 1, &&  \forall j \in J
\end{alignat}
\ref{myLabel}
\end{document}