Add arrowhead to plot: what is missing?

Question

In the MWE below, why do not have arrows in my plot?

\documentclass[12pt, border=1pc]{standalone}
\RequirePackage{tikz}
\RequirePackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}
\begin{axis}[axis x line=middle,
            axis y line=middle,,
            xtick={1.0, 3.0},
            ytick={1.0, 3.0},
            samples=100,
            xmin=-1,xmax=4.5,
            ymin=-1,ymax=4.5]
\addplot[domain={-1:4}]{x};
\addplot[domain={-1:4},
postaction={decorate,
decoration={markings,
    mark=at position 2 with {\arrow[thick]{>}},
    mark=at position 3 with {\arrowreversed[thick]{>}}}
}
]{((x-3)^2 * (x-1)^2) + x};
\end{axis}
\end{tikzpicture}
\end{document}

what do you want to accomplish exactly? arrows on both end of the curve? — anis, Jan 29 '24 at 11:22
Both that (though that part is not mentioned in the question) and at specific point(s). — blackened, Jan 29 '24 at 11:41
Does this answer your question: https://tex.stackexchange.com/questions/370875/add-arrowhead-to-plot — anis, Jan 29 '24 at 12:45
Yes I saw it; tried to replicate it, could not do it. So I must be doing something wrong. — blackened, Jan 29 '24 at 12:51
Note that you need to activate/apply the decoration using decorate. — Jasper Habicht, Jan 29 '24 at 13:27

score 1 · Accepted Answer · answered Jan 29 '24 at 14:31

Your range limits on Y combined with your marks positions are truncating the arrow.

I debugged it by commenting anything that is not necessary to have arrows to the plot.

    \begin{tikzpicture}
        \begin{axis}[axis x line=middle,
%           axis y line=middle,
%           xtick={1.0, 3.0},
%           ytick={1.0, 3.0},
%           samples=100,
%           xmin=-1,xmax=4.5,
%           ymin=-1,ymax=4.5,
            ]
%           \addplot[domain={-1:4}]{x};
            \addplot[domain={-1:4},
            postaction={decorate, decoration={
                markings,
                mark=at position 0.65 with {\arrow{>};}
            }}
            ]{((x-3)^2 * (x-1)^2) + x};
        \end{axis}
    \end{tikzpicture}

The arrow is exactly where I thought it would be 65% of the plotted curve.

By playing a bit with the code:

    \begin{tikzpicture}
        \begin{axis}[
%           axis x line=middle,
%           axis y line=middle,
%           xtick={1, 3.0},
%           ytick={1.0, 3.0},
            samples=100,
            xmin=-1,xmax=4,
            ymin=-1,ymax=4.5,
            ]                   
%           \addplot[domain={-1:4}]{x};
            \addplot[domain={-1:4.5},
            postaction={decorate, decoration={
                markings,
                mark=at position 0.65 with {\arrow{>};}
            }}
            ]{((x-3)^2 * (x-1)^2) + x};
        \end{axis}
    \end{tikzpicture}

Thank you. I do not understand this truncating business. In my example, for example, I npow did .85 and it worked, I see the arrow. I did .7, .75, .9, and I see no arrow. I am confused. — blackened, Jan 29 '24 at 14:59
My understanding is that the addplot command is executed before the axisenvironment limits the plot. So the curve is plotted. Then the arrow is positioned at x%. Then x or y limit truncates it. — anis, Jan 29 '24 at 15:01
https://tikz.dev/pgfplots/reference-specifyrange#autosec-5859. Check this option: update limits=true|false (initially true). — anis, Jan 29 '24 at 15:09
or changing the plotting tool to https://tikz.dev/dv-introduction — anis, Jan 29 '24 at 15:30

Add arrowhead to plot: what is missing?

1 Answers1