3

Today I am trying to reproduce several economic diagrams. Here is an example of a phase diagram:

enter image description here

I would like to use a tikzpicture environment. But I have no idea how to start creating the axis in relative length, so is there something like width=0.7\textwidth? How to define the size of this tikzpicture anyway? Better relative to the size of my A4 paper or in terms of pixel? Maybe someone can help with creating the plain diagram-axis and e.g. the \dot k line as well as some relation position point k^*.

I started for example this way:

\begin{center}
\begin{tikzpicture}[
    scale=5,
    axis/.style={very thick, ->, >=stealth'},
    important line/.style={thick},
    dashed line/.style={dashed, thin},
    pile/.style={thick, ->, >=stealth', shorten <=2pt, shorten
    >=2pt},
    every node/.style={color=black}
    ]
    \draw[axis] (-0.1,0)  -- (1.8,0) node(xline)[right] {$k_t \equiv \frac{K_t}{H_t}$};
    \draw[axis] (0,-0.1) -- (0,1.8) node(yline)[above] {$c_t \equiv \frac{C_t}{H_t}$};
    \draw[important line] (0.9,0.1) coordinate (C) -- (0.9,1.6)
        coordinate (C) node[above, text width=5em] {$\dot c = 0$};
\end{tikzpicture}
\end{center}

This yields: enter image description here

Is this a good way to model axis? How should I add a label k^*? I have to remember that I placed the c-line at 0.9?

Update: Applied solution.

\begin{center}
\begin{tikzpicture}[scale=2]
\tikzset{every picture/.style=semithick}
\begin{axis}[
  axis lines=left,
  xmin=0,
  xmax=2.2,
  ymin=0,
  ymax=2.2,
  clip=false,
  xtick={\empty},
  ytick={\empty},
    xlabel=$\small k_t \equiv \frac{K_t}{H_t}$,
    xlabel style={at={(current axis)}, yshift=-5.8cm, xshift=0.3cm},
    ylabel=$\small c_t \equiv \frac{C_t}{H_t}$,
    ylabel style={at={(current axis.north west)},rotate=-90,yshift=-19em, xshift=0.5cm},
]
\tiny % scale up entire tikz, scale down the font size
\addplot[no marks,domain=0.2:1.8] {-x+2}; % negative slope
\node[anchor=south] at (axis cs:0.2,1.8) {$\dot k = 0$}; % label of k0

\draw[dashed, gray] % k1 line
  (axis cs:0.25,0) node[below, black] {$k_1(\mu^{\ast})$} -- 
  (axis cs:0.25,1.5);
\draw[dashed, gray] % k2 line
  (axis cs:1.75,0) node[below, black] {$k_2(\mu^{\ast})$} -- 
  (axis cs:1.75,1.5);
\draw % c = 0 line
  (axis cs:1,0) node[below] {$k^{\ast}$} -- 
  (axis cs:1,2) node[above] {$\dot c=0$};
\draw[dashed,width=2em, gray] % c* line
  (axis cs:0,1) node[left, black] {$c^{\ast}$} -- 
  (axis cs:1,1);
\draw[myarr] % lower transition arrows
  (axis cs:0.4,0.4) -- 
  (axis cs:1,1);
\draw[myarr] % upper transition arrows
  (axis cs:1.6,1.6) -- 
  (axis cs:1,1);
\path % mini triangles
  pic at (axis cs:0.6,0.3) {coordsys} % down left
  pic[yscale=-1] at (axis cs:1.2,0.5) {coordsys} % down right
    pic[rotate=180] at (axis cs:1.4,1.8) {coordsys} % up right 
  pic[xscale=-1] at (axis cs:0.8,1.6) {coordsys}; % up left
\end{axis}
\normalsize
\end{tikzpicture}
\end{center}

I modified your code to fit my needs. I think now it's fine for me. Last think I can't resolve is to let x- and y-axis begin somehow -0.1 away from the origin. That's just cosmetic, but interesting though. Thanks!

enter image description here

  • Use pgfplots. – Gonzalo Medina Aug 14 '15 at 14:19
  • I think I do. I found some options like \draw[axis] (-0.1,0) -- (1.8,0) node(xline)[right] is this a good may of defining axis? – Mac Aug 14 '15 at 14:24
  • No, you're not using pgfplots, then there would have been \begin{axis} ... \end{axis} within your tikzpicture. Whether you have \usepackage{pgfplots} or not I can't say, but that diagram doesn't use its features. – Torbjørn T. Aug 14 '15 at 14:34
  • For your last question about the axis, use axis line style={shorten < = -0.5cm}. – Gonzalo Medina Aug 14 '15 at 21:48
  • This is exactly what I was looking for. Thanks again! – Mac Aug 21 '15 at 6:59
6

At this point it's hard to know whether pure TikZ or pgfplots is the best tool, since both packages allow to easily draw the diagram in the question. Below I show both possibilities.

If you need to plot some functions, then pgfplots would be my suggestion; if not, then pure TikZ can do the job.

In both cases, you can use the appropriate options to scale your diagram once you've drawn it. Using pgfplots, you have acces to the width=<lenght> and height=<lenght> options for the axis environment, allowing to control the final width and height of the plot. Using pure TikZ, on the other hand, you can set x=<lenght> and y=<lenght> (see code above) and this will also scale your diagram. In both cases you also have the scale=<factor> option too (although this will also scale the labels which might not be wanted).

In the example below I used pgfplots just for illustration; using the axis cs coordinate system you can place elements at designated locations; some decorations and pics and you're ready to go:

enter image description here

The code:

\documentclass[border=3pt]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{arrows,decorations.markings}

\tikzset{
  coordsys/.pic={
    \draw[->] (0,0) -- ++(6mm,0pt);
    \draw[->] (0,0) -- ++(0pt,6mm);
  },
  myarr/.style={decoration={
      markings,
      mark=between positions 0 and 1 step 4mm with {\arrow{stealth}},
    },
    postaction=decorate
  },
}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
  axis lines=left,
  xmin=0,
  xmax=2.2,
  ymin=0,
  ymax=2.2,
  clip=false,
  xtick={\empty},
  ytick={\empty}
]
\addplot[no marks,domain=0.2:1.8] {-x+2};
\draw[dashed]
  (axis cs:0.25,0) node[below] {$k_1(\mu^{\ast})$} -- 
  (axis cs:0.25,1.5);
\draw[dashed]
  (axis cs:1.75,0) node[below] {$k_2(\mu^{\ast})$} -- 
  (axis cs:1.75,1.5);
\draw
  (axis cs:1,0) node[below] {$k^{\ast}$} -- 
  (axis cs:1,2) node[above] {$\iota=0$};
\draw[dashed]
  (axis cs:0,1) node[left] {$c^{\ast}$} -- 
  (axis cs:1,1);
\draw[myarr]
  (axis cs:0.4,0.4) -- 
  (axis cs:1,1);
\draw[myarr]
  (axis cs:1.6,1.6) -- 
  (axis cs:1,1);
\path
  pic at (axis cs:0.3,0.3) {coordsys}
  pic[rotate=180] at (axis cs:1.7,1.7) {coordsys}
  pic[xscale=-1] at (axis cs:0.8,1.7) {coordsys}
  pic[yscale=-1] at (axis cs:1.2,0.3) {coordsys};
  \end{axis}
\end{tikzpicture}%

\end{document}

The same idea, but with pure TikZ now:

\documentclass[border=3pt]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{arrows,decorations.markings}

\tikzset{
  coordsys/.pic={
    \draw[->] (0,0) -- ++(6mm,0pt);
    \draw[->] (0,0) -- ++(0pt,6mm);
  },
  myarr/.style={decoration={
      markings,
      mark=between positions 0 and 1 step 4mm with {\arrow{stealth}},
    },
    postaction=decorate
  },
}

\begin{document}

\begin{tikzpicture}[x=3cm,y=3cm]
\draw[->]
  (-0.1,0) -- (2,0);
\draw[->]
  (0,-0.1) -- (0,2);
\draw[dashed]
  (0.25,0) node[below] {$k_1(\mu^{\ast})$} -- 
  (0.25,1.5);
\draw[dashed]
  (1.75,0) node[below] {$k_2(\mu^{\ast})$} -- 
  (1.75,1.5);
\draw
  (1,0) node[below] {$k^{\ast}$} -- 
  (1,2) node[above] {$\iota=0$};
\draw[dashed]
  (0,1) node[left] {$c^{\ast}$} -- 
  (1,1);
\draw[myarr]
  (0.4,0.4) -- 
  (1,1);
\draw[myarr]
  (1.6,1.6) -- 
  (1,1);
\path
  pic at (0.3,0.3) {coordsys}
  pic[rotate=180] at (1.7,1.7) {coordsys}
  pic[xscale=-1] at (0.8,1.7) {coordsys}
  pic[yscale=-1] at (1.2,0.3) {coordsys};
\end{tikzpicture}

\end{document}

enter image description here

If you use pgfplots, you have acces to the width=<lenght> and height=<lenght> options allowing to control the final width and height of the plot. Using pure TikZ, on the other hand, you can set x=<lenght> and y=<lenght> (see code above) and this will also scale your diagram. In both cases you also have the scale=<factor> option too.

| improve this answer | |
  • This is an incredible answer. I need some time to consider all the differences and check the code. Thanks a lot – Mac Aug 14 '15 at 14:56
  • @Mac You're welcome. In the last update to my answer I added some remarks about options allowing control on the width/height of the diagrams and I am not sure if you saw it. – Gonzalo Medina Aug 14 '15 at 15:04
  • Well, now I got the new questions to the pdfplot-version: I realize your version is too small for my purpose. When I try so scale up everything, the labels get too big. So after defining your absolute length for x and y axis (2.2) there is no chance e.g. to adjust this for 4.4 without changing all other coordinates by hand, right? So I have to think very carefully right at the beginning about the size of my picture? – Mac Aug 14 '15 at 15:22
  • @Mac No. Instead of scaling, you can pass width=0.7\textwidth for example to the axis options. – Gonzalo Medina Aug 14 '15 at 15:55

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