x=[-2,-1,1,2, 1,-1,-2,2]
    y=[-2,-1, 1, 2,-1,1,2,-2]
    S=[0.0020,0.0010,-0.0010,0.0020,0.0005,-0.0005,0.0005,-0.0005]

from pylab import *
    x=X2
    y=Y2
    z=S
    x,y=np.meshgrid(x,y)
    cf=contourf(x,y,z,linspace(-0.005,0.005,10))
    colorbar(cf)
    xlabel('x')
    ylabel('y')
    plt.show()