def GetFlux(self, time):

                bx = self.GetField("bx", time) * self.wpewce
                by = self.GetField("by", time) * self.wpewce
                bz = self.GetField("bz", time) * self.wpewce



                flux  = np.zeros((self.ncells[0]+1,self.ncells[1]+1),"float32", order='FORTRAN')
                flux2  = np.zeros((self.ncells[0]+1,self.ncells[1]+1),"float32", order='FORTRAN')

                dx = self.dl[0]
                dz = self.dl[1]

                nx = self.ncells[0]
                nz = self.ncells[1]

                j = 0

               for i in np.arange(1, nx):
                       flux2[i,0] = flux2[i-1,0] + bz[i-1,0]*dx

                flux[1:,0] = flux[0,0] + np.cumsum(bz[:-1,0]*dx)



               for j in np.arange(1,nz):
                       flux2[0,j] = flux2[0,j-1] - bx[0,j-1]*dz

                flux[0,1:] = flux[0,0] - np.cumsum(bx[0,:-1]*dz)


               for i in np.arange(1,nx):
                       for j in np.arange(1,nz):
                               flux2[i,j] = 0.5*(flux2[i-1,j] + bz[i-1,j]*dx) + 0.5*(flux2[i,j-1] - bx[i,j-1]*dz)


        # flux = ???


                return flux2