How to use the oommfc.Precession function in oommfc

def macrospin():
    """Return a sytsem that represents a macrospin.

    """
    p1 = (0, 0, 0)
    p2 = (5e-9, 5e-9, 5e-9)
    cell = (5e-9, 5e-9, 5e-9)
    mesh = oc.Mesh(p1=p1, p2=p2, cell=cell)

    system = oc.System(name='example-macrospin')
    system.hamiltonian = oc.Zeeman(H=(0, 0, 5e6))
    system.m = df.Field(mesh, value=(0, 0, 1), norm=8e6)
    system.dynamics = oc.Precession(gamma=oc.consts.gamma) + \
        oc.Damping(alpha=0.05)

    return system

def bar():
    system = oc.System(name="example-bar")
    shape = (100e-9, 30e-9, 30e-9)
    d = 10e-9
    mesh = oc.Mesh(p1=(0, 0, 0), p2=shape, cell=(d, d, d))
    # Permalloy
    A = 1e-12
    H = (0, 0, 0)  # no Zeeman field, but provide interaction as convenience

    system.hamiltonian = oc.Exchange(A=A) + oc.Demag() + oc.Zeeman(H=H)
    alpha = 0.2
    system.dynamics = oc.Precession(gamma=oc.consts.gamma0) + \
        oc.Damping(alpha=alpha)
    Ms = 8e6  # A/m
    system.m = df.Field(mesh, value=(1, 0, 1), norm=Ms)

    return system