from math import * from matplotlib.pyplot import * for i in range(1,13): for j in range(1,9): x,y=i-0.5,j-0.5 r=sqrt((x-6.0)**2+(y-4.0)**2) dx,dy=-(x-6.0)/r**3,-(y-4.0)/r**3 d=sqrt(dx**2+dy**2) dx,dy=dx/d,dy/d arrow(x-dx/2.0,y-dy/2.0,dx,dy) grid() show()