A=Uscharfettergummel(nodes,Nnodes,elements,Nelements,acoeff,bcoeff,v) Builds the Scharfetter-Gummel matrix for the the discretization of the LHS of the Drift-Diffusion equation: $ -(a(x) (u' - b v'(x) u))'= f $ where a(x) is piecewise constant and v(x) is piecewise linear, so that v'(x) is still piecewise constant b is a constant independent of x and u is the unknown