% m38_rectangle.m - Brownian walk in a 10x1 rectangle

close all
inside = @(x,y) find( (abs(x)<5) & (abs(y)<.5) );
outside = @(x,y) find( (abs(x)>= 5) | (abs(y)>=.5) );

  N = input('How many fleas (e.g. 5, 500)? ');
  x = zeros(N,1); y = zeros(N,1);
  h=fill([-5 5 5 -5 -5],[-.5 -.5 .5 .5 -.5],[1 1 1]);
  LW = 'linewidth'; set(h,LW,1)
  set(gcf,'position',[30 430 1450 115])
  axis([-5.3 5.3 -.53 .53]), hold on, axis off
  plot([-5 5 5 -5 -5],[-.5 -.5 .5 .5 -.5],'-k',LW,.6)
  plot(x,y,'.','markersize',18,'color','b');
  set(gca,'xtick',[],'ytick',[])
  shg
  drawnow
  pause
  ii = inside(x,y); oo = outside(x,y);
  ll = length(ii);
  while ll>0
    x(ii) = x(ii) + .025*sign(randn(ll,1));
    y(ii) = y(ii) + .025*sign(randn(ll,1));
    hold off
    h=fill([-5 5 5 -5 -5],[-.5 -.5 .5 .5 -.5],[1 1 1]);
    set(h,LW,1)
    set(gcf,'position',[30 430 1450 115])
    axis([-5.3 5.3 -.53 .53]), hold on, axis off
    plot([-5 5 5 -5 -5],[-.5 -.5 .5 .5 -.5],'-k',LW,.6)
    ii = inside(x,y); ll = length(ii); oo = outside(x,y);
    plot(x(ii),y(ii),'.','markersize',18,'color','b');
    plot(x(oo),y(oo),'.','markersize',18,'color','r');
    set(gca,'xtick',[],'ytick',[])
    drawnow
  end