[Tex/LaTex] Aligning multiple rows and columns with different number of equations (Align environment)

alignequations

I am trying to achieve the following structuring with an align environment:
Each of the first two rows has 2 equations, which should be aligned. In the third and fourth row, there should be one centered equation in each case.
With my approach those criteria are mainly satisfied, but the horizontal space is way to large and it looks somehow irregular. So I would like to ask how I can get the 3./4. row to be between the two equation in the first two lines.

\documentclass[a4paper]{article}
\usepackage{amsmath}

\begin{document}
    \begin{align}
        x1&=y1  &       a1&=b1 \label{eq:a} \\
        x2&=y2  &       a2&=b2 \label{eq:b} \\
    \begin{split}
        x3=y3 \\
        a3=b3
        \label{eq:c}
    \end{split}
    \end{align}
\end{document}

The following approach would be perfect, if there wasn't a blank line between the two align environments.

\begin{document}
    \begin{align}
        x1&=y1  &       a1&=b1 \label{eq:a} \\
        x2&=y2  &       a2&=b2 \label{eq:b}
    \end{align}
    \begin{align}
    \begin{split}   
        x3=y3 \\
        a3=b3
        \label{eq:c}
    \end{split} 
    \end{align}
\end{document}

I really hope you can understand my English 😀
Thanks in advance!

Best Answer

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  &  &  &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \begin{aligned}
         x3&=y3 \\
         a3&=b3
        \end{aligned}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  & \qquad\qquad & \qquad\qquad &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \mathclap{\begin{aligned}
         x3&=y3 \\
         a3&=b3
        \end{aligned}}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

The long third equation version:

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  & \qquad\qquad & \qquad\qquad &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \mathclap{\begin{aligned}
         x3&=y3 +a1 -d1 +e5 +a1 -d1 +e5 \\
         a3&=b3
        \end{aligned}}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

The centered long third equation version:

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
    \begin{alignat}{3}
        x1&=y1  & \qquad\qquad & \qquad\qquad &      a1&=b1 \label{eq:a} \\
        x2&=y2  & & &      a2&=b2 \label{eq:b} \\
        && \mathclap{\begin{gathered}
         x3=y3 +a1 -d1 +e5 +a1 -d1 +e5 \\
         a3=b3
        \end{gathered}}& &
        \label{eq:c}
    \end{alignat}
\end{document}

enter image description here

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