function xx=diffuse(period)
x=1:20;        		% x is the numbers 1 through 20
time=0;
const=.01;


tnew=zeros(1,20)+300;   % initial conditions of 300 deg everywhere
told=tnew;% we are going to need two separate temperature vectors in
          % order to simultaneously solve for the current temperature and
          % not overwrite the previous temperature

h=plot(tnew);  		% a cool way to animate plots
xlabel('distance')
ylabel('temperature')
axis([1 20 250 350])
set(h,'EraseMode','none','LineWidth',3)


while 1                                 % a MATLAB command to loop until
                                        % you press cntrl-C
  time=time+1;
  told(1)=300+30*sin(time/period*2*pi); % sinusoidally varying temperature
  tnew(1)=told(1);
					% at surface

% now solve the equation!
% tnew is the next time step of the temperature, told is the last time
%    step, and tnew-told is the second derivative of the temperautre
%    (the OLD temperature) in the spatial direction

  for i=2:19
    tnew(i)=told(i)+const*(told(i-1)+told(i+1)-2*told(i));
  end

% that was it! those 3 lines were the full solution to the differential
%  equation for a single time step.

  told=tnew; 	% make the old temp equal to the new temp to use during the
		% next go around

%  plot(tnew,'r')
%  plot(tnew,'b')
   set(h,'YData',tnew,'Color',[0,0,1])	% overplot a blue line
   set(h,'Color',[1,0,0])		% overplot a red line
   drawnow				% plot it!

end