# tikz not drawing the correct function

In an attempt to make a graphic of Gay-Lussacs Law, I made this graphic. I've managed to draw the measure points, but the function corresponding with it (which I did with my TI-nspire) is not drawing correctly. The intersection point with the y-axis is too low. It should be at 97.

\documentclass{beamer}
\usepackage{tikz,tkz-base, pgf,tkz-euclide}
\usetikzlibrary{arrows, calc,intersections,through,backgrounds,snakes, decorations.pathmorphing}
\usepackage{pgfplots}
\pgfplotsset{compat=1.8}

\begin{document}
\begin{frame}
\begin{tikzpicture}
\begin{axis}[%
title= Gay-Lussac,
major grid style=gray,
axis lines=center,
ymin=85,
ymax=125,
axis y discontinuity=crunch,
xmin=0, xmax=40,
xtick={0,5,...,40},
ytick={0,5,...,125},
width=\textwidth,
height=8cm,
xlabel={\tiny V (ml)},
ylabel={\tiny p (kPa)},
%ticks=both,
minor xtick={0,5,...,40},
minor ytick={0,5,...,125},
grid=both,
enlarge x limits={upper},
enlarge y limits={upper},
]
\draw[color=blue, very thick, samples=80, domain=0:410]    plot (\x,0.357355263*\x + 97)     node[above] {{\scriptsize  $V_1$}};
\addplot[color = black, fill  = black, mark  = *,  only marks]
coordinates{(20.016,103.19) (23.709,104.49) (24.707,105.06) (26.6,105.7) (27.8,106.2) (28.7,106.5) (30.4,107.2) (32.4,107.7) (34.6,108.5) (36.8,109.2) (38.2,109.5)};
\end{axis}
\end{tikzpicture}
\end{frame}
\end{document}


Use

\addplot[color=blue, very thick, samples=80, domain=0:410]   {0.357355263*x + 97}
node[above] {{\scriptsize  $V_1$}};


\draw[color=blue, very thick, samples=80, domain=0:410]
plot (\x,0.357355263*\x + 97)     node[above] {{\scriptsize  $V_1$}};


since you are using pgfplots anyway.

\documentclass{beamer}
\usepackage{tikz,tkz-base, pgf,tkz-euclide}
\usetikzlibrary{arrows, calc,intersections,through,backgrounds,snakes, decorations.pathmorphing}
\usepackage{pgfplots}
\pgfplotsset{compat=1.8}

\begin{document}
\begin{frame}
\begin{tikzpicture}
\begin{axis}[%
title= Gay-Lussac,
major grid style=gray,
axis lines=center,
ymin=85,
ymax=125,
axis y discontinuity=crunch,
xmin=0, xmax=40,
xtick={0,5,...,40},
ytick={0,5,...,125},
width=\textwidth,
height=8cm,
xlabel={\tiny V (ml)},
ylabel={\tiny p (kPa)},
%ticks=both,
minor xtick={0,5,...,40},
minor ytick={0,5,...,125},
grid=both,
enlarge x limits={upper},
enlarge y limits={upper},
]
\addplot[color=blue, very thick, samples=80, domain=0:410]   {0.357355263*x + 97}     node[above] {{\scriptsize  $V_1$}};
\addplot[color = black, fill  = black, mark  = *,  only marks]
coordinates{(20.016,103.19) (23.709,104.49) (24.707,105.06) (26.6,105.7) (27.8,106.2) (28.7,106.5) (30.4,107.2) (32.4,107.7) (34.6,108.5) (36.8,109.2) (38.2,109.5)};
\end{axis}
\end{tikzpicture}
\end{frame}
\end{document}


• Thanks for your answer. I used this option because I couldn't put a node to it, but that you answered also. :) But it is still strange it doesn't draw the correct function. – Arne Timperman Jan 18 '15 at 13:03