% free-fall.tex — single-stock numerical model.
%
% A ball dropped from y0 = 100 m under constant gravity.  One
% Forrester stock for height (Y), one for velocity (V), and an
% auxiliary integrator for time (T).  \diagrammodel renders Y(T).

\documentclass{article}
\usepackage[syntax=english]{numodel}

\begin{document}

\newmodelprefix{ball}

\mvar{T}{t}{0}{\s}{2}{systeem}
\mvar{Dt}{dt}{0.05}{\s}{2}{systeem}
\mvar{V}{v}{0}{\m\per\s}{3}{voorraad}
\mvar{Y}{y}{100}{\m}{3}{voorraad}
\mvar{G}{g}{-9.81}{\m\per\s\squared}{3}{constante}

\mrule{V}{\ballV + \ballG * \ballDt}
\mrule{Y}{\ballY + \ballV * \ballDt}
\mrule{T}{\ballT + \ballDt}
\mstop{\ballY <= 2}

\section*{Tekstmodel}
\textmodel

\section*{Grafisch Model}
\graphicmodel
\directlua{
local f = io.open("free-fall.layout.txt","w")
f:write(numodel.dump_layout("ball")); f:close()
}

% Simulatie
\computemodel

\section*{Diagram}
\def\ycmmax{8}
\diagrammodel{T}{Y}{ball-fall}

\end{document}