Dear Anton,
Thank you for quick response; sorry,  I mean the graph does appear but the conductance data are all zeros (see below).

data = []
energies = [-2 * pot + 4. / 50. * pot * i for i in xrange(51)]
for energy in energies:
    smatrix = kwant.smatrix(sys, energy)
    data.append(smatrix.transmission(0, 1))
print data
pyplot.figure()
pyplot.plot(energies, data)
pyplot.xlabel("energy [t]")
pyplot.ylabel("conductance [e^2/h]")
pyplot.show()

[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

Best Regards,

Dedi 
> From: anton.akhmerov@gmail.com
> Date: Sun, 27 Sep 2015 13:38:35 +0200
> Subject: Re: [Kwant] Conductance Plot doesn't appear
> To: setiabudidaya@hotmail.com
> CC: kwant-discuss@kwant-project.org
>
> Dear Dedi,
>
> I believe your problem is rather related to the jupyter/ipython
> notebook. Do regular plots appear? What if you add a pyplot.show() to
> the cell?
>
> Best,
> Anton
>
> On Sun, Sep 27, 2015 at 12:17 PM, Dedi Setiabudidaya
> <setiabudidaya@hotmail.com> wrote:
> > Can anyone help me why the conductance plot in the enclosed graphene code
> > doesn't appear ?
> > I just copied the codes from the tutorial. Thank you in advance.