fdirout = 'ppmmovie';
  fbaseout = 'movie';

  dt = 0.1;

  x = [-1 : 2/16 : 1];
  y = x;
  [X, Y] = ndgrid (x, y);

  for n = 0 : 16
    t = n * dt;

    Z = 0.1 + 0.9 * exp(- (X.^2+Y.^2) / (2*t));
    h = mesh (X, Y, Z);
    caxis ([0 1]);
    title (['time t = ', num2str(t)]);

    filename = [fdirout, '/', fbaseout, int2str(n), '.ppm'];
    print ('-dppmraw', filename);
  end;