# Re: [Kwant] (no subject)

```Dear Kumar,

To do so you need to put a potential in all the leads (you can fix one of
them  to zero) and then use the Conductance matrix.```
```
You will search for V1, V2, (V3=0) such that I1=-I2 and I3=0

(I1,-I1,0)^T  = G   (V1,V2,0)^T

T is the transpose, G is the Conductance matrix

G is singular so to solve this equation, you invert a submatrix of G

def get_Voltage(energy, params, I1=1):

SM=kwant.smatrix(sysf,energy=energy,params=params))
G=SM.conductance_matrix()
M=linalg.inv(G[0:2,0:2])
V=M@array([I1,-I1]).T
return V

I hope this helps.

On Fri, Aug 10, 2018 at 9:31 AM, Rohit Kumar Srivastav <
rohit.srivas...@snu.edu.in> wrote:

> I want to apply a voltage on the stadium with three leads in such a way
> two leads constitute the same current and one lead constitute zero current
> (Its means voltage is zero in this lead always) for calculating the
> scattering matrix.
> Please, suggest me what is the code of voltage. (How to apply the voltage)
> Best,
> Rohit
>

--