%% mPICm13.m  (figure 13)
%% mathsPIC  small spiral by recursion
%%  (requires file mPICm13.dat)
\documentclass[a4paper]{article}
\usepackage{pictexwd}
\begin{document}
%%---------------
\beginpicture
paper{units(mm), xrange(0,60), yrange(0,60)}% axes(LB), ticks(10,10)}
point(C){30,30}   % circle center
drawcircle(c,25)
variable(a){315}  % angle
variable(r){20}   % radius
variable(s){5}    % square semi-diagonal
point(t){c,polar(r,330 deg)}
inputfile(mpicm13.dat)[30]
\endpicture
%%----------------
\end{document}