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I have the plot of a line using pgfplots and the plot of the same line using TikZ. I would like them to be identical.

I need to correct a mistake in the plot of a line using pgfplots. The point that is plotted should be at the point (a, ma+b). Since a=-3 and m=-0.5=b, the point as specified in the code is (-3,-2). Why is the point not plotted correctly?

In the plot of a line using TikZ, I need to put the label "y = mx + b" in the right place. (Look at the other plot.) I also need to add two tick marks - one on the x-axis at -3 and one on the y-axis at -2. I was told that there was a default option for tick marks. (I was not able to view the datavisualization library as described in chapter 75 of the manual at the following web site: texdoc.net/texmf-dist/doc/generic/pgf/pgfmanual.pdf .)

\documentclass[10pt]{amsart}
\usepackage{tikz}
\usetikzlibrary{calc,angles,positioning,intersections,quotes,decorations.markings}
\usepackage{mathtools}

\usepackage{pgfplots}


\begin{document}
\noindent \hspace*{\fill}
\begin{tikzpicture}
\begin{axis}[width=5in,axis equal image,
    axis lines=middle,
    xmin=-5,xmax=5,samples=201,
    xlabel=$x$,ylabel=$y$,
    ymin=-3.5,ymax=2.5,
    restrict y to domain=-3.5:2.5,
    enlargelimits={abs=0.5cm},
    axis line style={latex-latex},
    ticklabel style={font=\tiny,fill=white},
    xtick={\empty},ytick={\empty},
    extra x ticks={-3},
    extra x tick labels={$a$},
    extra y ticks={-2},
    extra y tick labels={$ma+b$},
    yticklabel style={anchor=west},
    yticklabel shift=-4pt,
    xlabel style={at={(ticklabel* cs:1)},anchor=north west},
    ylabel style={at={(ticklabel* cs:1)},anchor=south west}
]

\addplot[latex-latex,samples=201,domain=-5:5,blue] {0.5*x - 0.5} node[above left, pos=0.9,font=\footnotesize]{$y = mx + b$};
\draw [fill] (-3,-2) circle [radius=1.5pt];
\end{axis}
\end{tikzpicture}
\hspace*{\fill}
\vskip0.25in

\noindent \hspace*{\fill}
\begin{tikzpicture}
\draw[draw=gray!30,latex-latex] (0,2.5) +(0,0.5cm) node[above right] {$y$} -- (0,-3.5) -- +(0,-0.5cm);
\draw[draw=gray!30,latex-latex] (-5,0) +(-0.5cm,0) -- (5,0) -- +(0.5cm,0) node[below right] {$x$};
\draw[blue,domain=-5:5,samples=2,latex-latex] plot (\x, 0.5*\x - 0.5) node[above left, pos=0.9,font=\footnotesize]{$y = mx + b$};
\end{tikzpicture}
\hspace*{\fill}
\vskip0.25in

\end{document}

closed as off-topic by Stefan Pinnow, Zarko, Mensch, user36296, Arun Debray Jun 15 '17 at 21:37

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  • 5
    When you use normal TikZ commands like \draw inside an axis environment, you should either use the axis cs: coordinate system (so \draw [fill] (axis cs:-3,-2) circle [radius=1.5pt];), or set \pgfplotsset{compat=1.11} (or newer), which activates the axis cs coordinate system. – Jake Feb 26 '15 at 17:32
  • 1
    I think you can't place nodes on a plot using the pos syntax in plain TikZ, you'll need to either move it manually or draw the plot using a normal path. Just out of curiosity: why do you need to find two ways of achieving the same output? – Jake Feb 26 '15 at 19:54
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    No, you don't. That's what I meant in my first comment, either use axis cs or compat=1.11. Then you said "I added compat=1.11", then you asked me again how to put the dot in the right place, so I assumed that for some reason that approach didn't work for you. – Jake Feb 27 '15 at 20:13
  • 1
    By "normal path", I meant using \draw[blue,latex-latex] (-5,-3) -- (5,2) node[above left, pos=0.9,font=\footnotesize]{$y = mx + b$}; instead of \draw[blue,domain=-5:5,samples=2,latex-latex] plot (\x, 0.5*\x - 0.5) node[above left, pos=0.9,font=\footnotesize]{$y = mx + b$}; (so using the -- syntax instead of plot). The datavisualization library is described in chapter 75 of TikZ version 3.0. You're probably using 2.1? – Jake Mar 5 '15 at 18:19
  • 4
    I'm voting to close this question because it is solved in the comments. – Stefan Pinnow Jun 15 '17 at 20:00

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