n = 10;
x = -n:n;
y = -n:n;
[ X, Y ] = meshgrid ( x, y );
T = zeros ( 2 * n + 1, 2 * n + 1 );
for i = 1 : 50
  if ( i == 1 )
    T(n+1,n+1) = 10000;
  else
    T = walker_2d_update ( T );
  end
% surf ( X, Y, T );
  contourf ( X, Y, T );
  pause
end
