# Tikz Graph naming

This is a graph picture, what I would like to ask you is how to name "s_1" as same as "s_2", it means if you compile this, then you can see "s_1" is positioned at the right of the curve I would like to change naming as "s_2".

Also, how can I put "T" at (0,T)?

\documentclass[10pt]{beamer}
\usepackage{tikz}

\begin{document}

\begin{frame}{}

\frametitle{Key lemmas}

\framesubtitle{The weak maximum (minimum) principle}

For two continuous curves $s_1$, $s_2$ such that $s_1(t)<s_2(t), t\in[0,T]$, let us set $\displaystyle E_T:=\{(x,t): s_{1}(t)<x<s_{2}(t),\ 0<t\leq T\}$ and $\displaystyle B_T:=\{(s_{i}(t),t): 0\leq t\leq T,\ i\in\{1,2\}\}\cup\{(x,0): s_{1}(0)< x< s_{2}(0)\}$.

\begin{tikzpicture}

\draw[help lines, color=gray!30, dashed]  ;

\draw[->,] (-4,0)--(5.5,0) node[right]{$x(position)$};

\draw[->,](0,0)--(0,3) node[above]{$t(time)$};

\draw[scale=1,domain=1:4,smooth,variable=\x,red,ultra thick] plot ({\x},{\x-1}) node[right]{$s_2$};

\draw [scale=1,domain=-2:-0.5,smooth,variable=\x,red,ultra thick] plot ({\x},{(-2)*\x-1}) node[left]{$s_1$};

\draw[scale=1,domain=-0.5:1,smooth,variable=\x,red,ultra thick] plot ({\x},{0});

\draw[scale=1,domain=-3:5.5,smooth,variable=\x,blue,dashed] plot ({\x},{2});

\end{tikzpicture}

\end{frame}

\end{document}

• I am a bit confused about your question. You already have a label on your y-axis, and what prevents you from just replace s_1 in the tikzpicture by s_2? – user121799 May 5 '18 at 6:39
• It's about indication what is s_1. "s_1" is printed on the right side of it's curve I want to change it like s_2. – Jimmy May 5 '18 at 7:16
• I honestly do not understand what you mean. Can you draw a sketch in for example Paint, to illustrate? For the T, I guess \node[above right] at (0,2) {(0,T)};? – Torbjørn T. May 5 '18 at 7:40
• If you compile this, you will notice what I mean easily. I want to indicate which curve by s_1, s_2 but s_1 is not printed like s_2 at the end of curve. – Jimmy May 5 '18 at 7:47

Like this?

The key change is to swap the order of the domain in the first \draw .. plot. That is, use domain=-0.5:-2 instead of domain=-2:-0.5. When you append node {..} at the end of a \draw plot like that, the node is placed at the last plotted point. By swapping the order in the domain specification, the leftmost point is plotted last, so the s_1 node ends up where you see in the image.

(In a normal path, like \draw (0,0) -- (2,2);, you could have used pos=0 in the node options to move the node to the start of the path, but that doesn't work for a plot.)

I removed some unnecessary stuff from your code. variable=\x is default, so you don't have to specify it, and smooth is pointless for linear functions. scale=1 didn't seem necessary either.

\documentclass[10pt]{beamer}
\usepackage{tikz}
\begin{document}

\begin{frame}
\frametitle{Key lemmas}
\framesubtitle{The weak maximum (minimum) principle}

For two continuous curves $s_1$, $s_2$ such that $s_1(t)<s_2(t), t\in[0,T]$,
let us set $\displaystyle E_T:=\{(x,t): s_{1}(t)<x<s_{2}(t),\ 0<t\leq T\}$ and
$\displaystyle B_T:=\{(s_{i}(t),t): 0\leq t\leq T,\ i\in\{1,2\}\}\cup\{(x,0): s_{1}(0)< x< s_{2}(0)\}$.

\begin{tikzpicture}[samples=2]

\draw [->] (-4,0) -- (5.5,0) node[right]{$x$ (position)};
\draw [->] (0,0) -- (0,3) node[above]{$t$ (time)};

% the domain is changed in the following line
\draw [domain=-0.5:-2,red,ultra thick] plot ({\x},{(-2)*\x-1}) node [left]  {$s_1$};
\draw [domain=-0.5:1,red,ultra thick]  plot ({\x},{0});
\draw [domain=1:4,red,ultra thick]     plot ({\x},{\x-1})      node [right] {$s_2$};

\draw [domain=-3:5.5,blue,dashed]      plot ({\x},{2});

\node [above right] at (0,2) {(0,T)};

\end{tikzpicture}
\end{frame}
\end{document}

• @Jimmy No worries. As a sidenote, with a simple graph like that you could perhaps just as well do \draw [red,ultra thick] (-2,3) node [left] {$s_1$} -- (-0.5,0) -- (1,0) -- (4,3) node [right] {$s_2$};. – Torbjørn T. May 5 '18 at 12:30