This aims at supporting latex users with some tikz experience to draw system dynamics (SD) diagrams in his/her latex documents.

1. Add the following line to your preamble:

   \usepackage{systemdynamics}
   

2. Compile using pdflatex. Make sure the systemdynamics.sty file is somewhere where your latex distribution will find it.

The package provides tikz styles and shortcuts.

To draw a stock with the internal name nodename and the label nodelabel use the command:

\node (nodename) [stock] {nodelabel};

To position the node relative to an existing node, you can use the familiar positoning commands inside the [], i.e.

\node (nodename) [stock, below=1em of othernode] {nodelabel};

To add positive or negative flows with the label flowlabel to the node stockname, use the following commands:

\flowIn{stockname}{flowlabel}

\flowOut{stockname}{flowlabel}

This will create nodes with names in_stockname or out_stockname respectively.

To create a system dynamics variable with name varname and label varlabel, use the command

\node (varname) [sdvariable]  {varlabel};

To indicate relationships, use the \sdarrow command:

\sdarrow{fromNode}{toNode}{bend left=5}

The last argument is optional and contains tikz options that will be passed directly to tikz to control the arrow curvature etc.

You can use the node names of existing stocks, flows and variables to define start and end of the arrow. To avoid arrows that overlap with the node labels, the flows have additional points that can be used as start or endpoints of sdarrows:

• in_stock_down: A node below the incoming flow label
• in_stock_down_nolabel: A node below the incoming flows hourglass (useful if the flow has no label)
• in_stock_up: A node above the incoming flows hourglass
• out_stock_down: A node below the outcoming flow label
• out_stock_down_nolabel: A node below the outcoming flows hourglass (useful if the flow has no label)
• out_stock_up A: node above the outcoming flows hourglass

The following code draws a simple two-state diagram.

\documentclass{standalone}
\pagestyle{empty}
\usepackage{systemdynamics}

\begin{document}
\begin{tikzpicture} 

% Predator population
\node (predator) [stock] {Predator};
\flowIn{predator}{}
\flowOut{predator}{}
\sdarrow{predator}{out_predator_up}{bend left=70}

% Prey population
\node (prey) [stock, below=7em of predator, xshift=1em] {Prey};
\flowIn{prey}{}
\flowOut{prey}{}
\sdarrow{prey}{in_prey_down_nolabel}{bend left=70}

%Meetings
\node (meetings) [sdvariable, below=3em of predator, xshift=0.5em]  {Meetings};
\sdarrow{prey}{meetings}{bend left=5}
\sdarrow{predator}{meetings}{bend left=10}
\sdarrow{meetings}{in_predator_down_nolabel}{bend left=10}
\sdarrow{meetings}{out_prey_up}{bend left=10}

\end{tikzpicture}
\end{document}

The output will look as follows: