close all

x = [-100:100];
y = [-100:100];
[x,y] = meshgrid(x,y);

f    =  2;
toff = .2;
v    = 100;

  for t=0:.01:1

    e =  cos(2*pi*f*(t+x/v)).*(x<0).*(x>-v*t).*(x<-v*(t-toff)) +...
         cos(2*pi*f*(t-x/v)).*(x>=0).*(x<v*t).*(x>v*(t-toff));

    surf(x,y,e)
    axis([-100 100 -100 100 -1 1])
    caxis([-1 1])
    shading interp
    drawnow

    if t==0
      pause
    end

end