def GetAz(Bx, By, Jz, Nc, dl):
mesh = Grid2D(dx=dl[0], dy=dl[1], nx=Nc[0], ny=Nc[1])
_Az = CellVariable(mesh=mesh, value=0.0)
_Bx = CellVariable(mesh=mesh)
_Bx.value = np.reshape(Bx, Nc[0] * Nc[1], order='F')
_By = CellVariable(mesh=mesh)
_By.value = np.reshape(By, Nc[0] * Nc[1], order='F')
_Jz = CellVariable(mesh=mesh)
_Jz.value = np.reshape(Jz, Nc[0] * Nc[1], order='F')
_Az.equation = (DiffusionTerm(coeff=1.0) + _Jz == 0)
# beware of the sign of the flux : always consider outward direction
BCs = [
FixedFlux(value=_By.getFaceValue(), faces=mesh.getFacesLeft()),
FixedFlux(value=-_By.getFaceValue(), faces=mesh.getFacesRight()),
FixedFlux(value=-_Bx.getFaceValue(), faces=mesh.getFacesBottom()),
FixedFlux(value=_Bx.getFaceValue(), faces=mesh.getFacesTop())
]
_Az.equation.solve(var=_Az, boundaryConditions=BCs)
Az = np.reshape(_Az.value, Nc, order='F')
return Az
