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.. Hundekurve
function man(t)
## return t|-ones(size(t));
return cos(t)|sin(t);
endfunction
function dgl (t,y)
delta=man(t)-y;
norm=sqrt(sum(delta*delta));
return delta/norm;
endfunction
function mandog (t)
## Compute the dog curve at time t starting from 0.
## The dog starts in 0 and moves with speed 1.
## The mans movement is returned from function man
return heun("dgl",t,[0,0]);
endfunction
function show (endtime)
t=linspace(0,endtime,100);
y=heun("dgl",t,[0,0]);
m=man(t')';
xplot(y[1]_m[1],y[2]_m[2]);
title("Dog and Man");
wait(180);
xplot(y[1]-m[1],y[2]-m[2]);
title("Difference");
wait(180);
n=length(y[1]); d=sqrt((y[1,n]-m[1,n])^2+(y[2,n]-m[2,n])^2);
"Last difference : ", d,
return plot();
endfunction
show(3);
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