%

%  Plot solution to one-dimensional advection equation
%    u_t + c*u_x = 0,   -1<x<2,  t>0,
%    u(x,0) = f(x),     -1<x<2.

  x = [-1:.01:2]';
  t = [0:.01:1]';
  [X,T] = meshgrid(x,t);
  u = zeros(size(X));

  c = input(' Wave speed = ');
  sigsq = .01;
  for i = 1:max(size(t))
     ti = t(i);
     zi = X(i,:) - c*ti;
     ui = exp(-zi.^2/sigsq);

     %  Plot solution at time ti.

     figure(1)
     plot(x,ui)
     xlabel('x axis')
     ylabel('u')
     hdr = ['Solution at time t = ', num2str(ti)];
     title(hdr)
     drawnow
     pause(.01)
     u(i,:) = ui;
  end

%  Generate surface and contour plots of u vs x and t.

  figure(2)
  mesh(t,x,u')
  xlabel('t axis')
  ylabel('x axis')
  zlabel('u(x,t)')
  title('Surface plot of u vs x and t')
  colorbar

  figure(3)
  contour(t,x,u')
  xlabel('t axis')
  ylabel('x axis')
  title('Contour plot of u vs x and t')
  colorbar