%  Animation of a pressure wave reflecting from a partially 
%  absorptive wall.   Input is the absorption coefficient (alpha)
%  9/20/2000 J Lamancusa
%
c=343.;
freq=50;
lambda=c/freq;
alpha=input('alpha = ')
refl=sqrt(1.0-alpha)
w=2*pi*freq;
k=w/c;
xmax=1.75*lambda;
x=linspace(0,xmax,100);
npts=80 %80 points is one complete cycle
M=moviein(npts);
figure;
for n=1:npts;
   t=n/2000.;
   a=k*x-w*t;
   b=k*x+w*t;
   y=sin(a);
   z=refl*sin(b);
   sum=(y+z);
   plot(x,y,'r-',x,z,'g-',x,sum,'b-');
   axis([0 xmax -2.0 2.0]);
   h=uicontrol('Style','Pushbutton','Position',[5  0  80 30],...
        'Callback','hold off','String','Hold Off');
   h=uicontrol('Style','Pushbutton','Position',[95  0  80 30],...
      'Callback','hold on','String','Hold On');
	h=uicontrol('Style','Pushbutton','Position',[450  0  80 30],...
   'Callback','close','String','QUIT');

   M(:,n)=getframe;
      
   %drawnow;
end;

xlabel('Distance from Driver (meters)')
ylabel('Sound Pressure (Pa)')
S=['50 Hz    ','ALPHA = ',num2str(alpha), '   REFL = ',num2str(refl)]
title(S)
text('position',[12.4  -2.0],'string','WALL','FontWeight','bold', 'rotation',90)
text('position',[ -1.0 -2.0],'string','DRIVER','FontWeight','bold','rotation',90)
movie(M,1);
fig=figure('position',[100   100   300  200]);
map= get(fig,'colormap');
%mpgwrite(M,map,'wave_movie',[1 0 1 0 10  8  10 25]);