[pgfplot] Linea che attraversa due grafici

Puoi contrassegnare i punti che ti interessano, ricordarli con l’opzione [tt]remember picture[/tt] e disegnare in [tt]overlay[/tt] la retta che collega i due punti. `\documentclass

{standalone}
\usepackage{pgfplots}
\usepackage{kpfonts}

\pgfplotsset{every axis/.append style={
axis x line=bottom,
axis line style={->},
%xlabel={$\rho$},
axis lines = middle,
xtick = \empty,
ytick = \empty,
every axis x label/.style={at={(axis description cs:1,0)},anchor=west},
every axis y label/.style={at={(axis description cs:0,1)},anchor=east},
fai sparire le etichette/.style={
xtick style={opacity=0},
xticklabel style={opacity=0},
}
}
}

\tikzset{>=stealth}
\begin{document}

\begin{tikzpicture}[remember picture]
%\useasboundingbox (-0.5,-0.5) rectangle (7.5,6);
\begin{axis}[
ylabel=$\alpha_1(t)$,
xmin=0,xmax=5,
% ymin=0,
ymax=1.5,
xtick = {0.5, 1,2,3,4},
xticklabels = {$\overline{\alpha}_1$, $T_1$, $2T_1$, $3T_1$, $4T_1$},
%ytick = {5},
% yticklabels = {$\varphi_m$}%,
% xtick style={opacity=0},
%xticklabel style={opacity=0}
]
\addplot[domain = 0:0.5]{1};
\addplot[domain=0.5:1]{0};
\draw (axis cs: 0.5,1) — (axis cs:0.5,0);

\draw (axis cs: 1,1)–(axis cs:1,0);
\addplot[domain = 1:1.5] {1};
\addplot[domain = 1.5:2] {0};
\draw (axis cs: 1.5,1)–(axis cs:1.5,0);

\draw (axis cs: 2,1)–(axis cs:2,0);
\addplot[domain = 2:2.5] {1};
\addplot[domain = 2.5:3] {0};
\draw (axis cs: 2.5,1)–(axis cs:2.5,0);

\draw (axis cs: 3,1)–(axis cs:3,0);
\addplot[domain = 3:3.5] {1};
\addplot[domain = 3.5:4] {0};
\draw (axis cs: 3.5,1)–(axis cs:3.5,0);
%\draw[dotted] (axis cs: 4,0)–(axis cs: 4,5);
%\draw (axis cs: 0.45, 0.45*5) — (axis cs: 0.6, 0.45*5) — (axis cs: 0.6, 0.6*5) node

{$v$};

\node[coordinate] (start-retta) at (axis cs:3,0){};
\draw[red] (axis cs:3,0)–(axis cs:3,8);

\end{axis}
\end{tikzpicture}

\begin{tikzpicture}[remember picture]
%\useasboundingbox (-0.5125,-0.5) rectangle (7.5,6);
\begin{axis}[
ylabel = $\alpha_2(t)$,
ymin=0,ymax=1.5,
xmin=0,xmax=5,
xtick = {0.5, 1, 1.5, 2.5,3.5},
xticklabels = {$\overline{\alpha}_2$, $T_2$, $T'_2$, $T''_2$, $T'''_2$},
%xmin=0,xmax=5,
%ymin=0,ymax=6,
%ytick = {5},
% yticklabels = {$\varphi_m$}
]
\addplot[domain = 0:0.5]{1};
\addplot[domain=0.5:1]{0};
\draw (axis cs: 0.5,1) — (axis cs:0.5,0);

\draw (axis cs: 1,1)–(axis cs:1,0);
\addplot[domain = 1:1.25] {1};
\addplot[domain = 1.25:1.5] {0};
\draw (axis cs:1.25,1)–(axis cs:1.25,0);

\draw (axis cs: 1.5,1)–(axis cs:1.5,0);
\addplot[domain = 1.5:2] {1};
\addplot[domain = 2:2.5] {0};
\draw (axis cs:2,1)–(axis cs:2,0);

\draw (axis cs: 2.5,1)–(axis cs:2.5,0);
\addplot[domain = 2.5:3] {1};
\addplot[domain = 3:3.5] {0};
\draw (axis cs: 3,1)–(axis cs:3,0);

\draw (axis cs: 3.5,1)–(axis cs:3.5,0);
\addplot[domain = 3.5:4] {1};
\addplot[domain = 4:4.5] {0};
\draw (axis cs: 4,1)–(axis cs:4,0);

% \draw (axis cs: 2.5, 5 – 1.5*5/3) — (axis cs: 2.25, 5-1.5*5/3) — (axis cs: 2.25 ,5-1.25*5/3) node

{$w$};

\node[coordinate] (end-retta) at (axis cs:3,0){};
\end{axis}
\end{tikzpicture}

\begin{tikzpicture}[remember picture,overlay]
\draw[red] ([yshift=-0.5cm]start-retta)–(end-retta); % la retta non sovrascrive l'etichetta sull'asse x
\end{tikzpicture}

\end{document}`

Ciao
Claudio