'''Class for calculating the potential in a semi-infinite slice of neural tissue.
Set-up:


          SALINE -> sigma_3 = [sigma_3x, sigma_3y, sigma_3z]

<----------------------------------------------------> x = + a

          TISSUE -> sigma_2 = [sigma_2x, sigma_2y, sigma_2z]


               o -> charge_pos = [x,y,z]


<-----------*----------------------------------------> x = -a               
             \-> elec_pos = [x,y,z] 

             ELECTRODE -> sigma_3 = [sigma_3x, sigma_3y, sigma_3z]
    


'''