Nhiều đồ thị trong một lưới với groupplots

\documentclass{article}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\begin{document}
\begin{tikzpicture}
  \begin{groupplot}[
      group style={group size=2 by 1, horizontal sep=1.5cm},
      width=6cm, height=4.5cm, xlabel=$t$,
    ]
    \nextgroupplot[title={Position}, ylabel=$x$]
    \addplot[blue, thick, domain=0:4, samples=40] {x^2/2};
    \nextgroupplot[title={Velocity}, ylabel=$v$]
    \addplot[red, thick, domain=0:4] {x};
  \end{groupplot}
\end{tikzpicture}
\end{document}

\documentclass{article}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\begin{document}
\begin{tikzpicture}
  \begin{groupplot}[
      group style={
        group size=2 by 2,
        horizontal sep=1.2cm, vertical sep=1cm,
        xlabels at=edge bottom, ylabels at=edge left,
        xticklabels at=edge bottom,
      },
      width=5.5cm, height=4cm,
      xlabel=$t$, ylabel=$y$, domain=0:6, samples=50,
    ]
    \nextgroupplot \addplot[blue] {sin(deg(x))};
    \nextgroupplot \addplot[red] {cos(deg(x))};
    \nextgroupplot \addplot[teal] {exp(-x/2)};
    \nextgroupplot \addplot[orange] {x/6};
  \end{groupplot}
\end{tikzpicture}
\end{document}

\documentclass{article}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\begin{document}
\begin{tikzpicture}
  \begin{groupplot}[
      group style={group size=1 by 2, vertical sep=0.4cm, xticklabels at=edge bottom},
      width=8cm, xmin=0, xmax=5,
    ]
    \nextgroupplot[height=5cm, ylabel={Signal}]
    \addplot+[only marks] coordinates {(1,2.1) (2,3.9) (3,6.2) (4,7.8)};
    \addplot[red, domain=0:5] {2*x};
    \nextgroupplot[height=3cm, xlabel=$x$, ylabel={Residual}, ymin=-0.5, ymax=0.5]
    \addplot+[only marks] coordinates {(1,0.1) (2,-0.1) (3,0.2) (4,-0.2)};
    \addplot[gray, dashed, domain=0:5] {0};
  \end{groupplot}
\end{tikzpicture}
\end{document}