[Tex/LaTex] Tikz-Diagram: How to define relative positions for arrows, straight lines and labels

diagramspositioningtikz-pgf

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

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:

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!

Best Answer

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:

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}

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.

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

[Tex/LaTex] Numerical conditional within tikz keys

I am definitely unfamiliar with both beamer and tikz (do not quite get what the \only are supposed to do) but perhaps this could go in the direction you want:

\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{chains}
\newcounter{count}

% helper macro:
\long\def\GobToSemiColon #1;{}

\newcommand\myPicture{
\begin{tikzpicture}
  \begin{scope}[start chain = going below]
  \ifnum\value{count}<1 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>3 \expandafter\GobToSemiColon\fi
  \node[draw, rectangle, on chain] {display only when counter is between
    1 and 3};

  \ifnum\value{count}>-1 \expandafter\GobToSemiColon\fi
  \node[draw, rectangle, on chain] {display only when counter is
    negative}; 

  \ifnum\value{count}<100 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>200 \expandafter\GobToSemiColon\fi  
  \node[draw, rectangle, on chain] {display only if counter is between
    100 and 200};

  \ifnum\value{count}<3 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>20 \expandafter\GobToSemiColon\fi
  \node[draw, circle, on chain] {only when counter is in the range 3 to 20};
  \end{scope}
\end{tikzpicture}
}

\begin{document}
\begin{frame}
\only{\setcounter{count}{-3}\myPicture}
\only{\setcounter{count}{105}\myPicture}
\only{\setcounter{count}{39}\myPicture}
\only{\setcounter{count}{2}\myPicture}
\only{\setcounter{count}{5}\myPicture}
\end{frame}
\end{document}

beamer

Best Answer

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

[Tex/LaTex] Numerical conditional within tikz keys

Related Question