--- /dev/null
+function A=Uscharfettergummel(nodes,Nnodes,elements,Nelements,acoeff,bcoeff,v)
+
+%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
+%
+
+ ## This file is part of
+ ##
+ ## SECS1D - A 1-D Drift--Diffusion Semiconductor Device Simulator
+ ## -------------------------------------------------------------------
+ ## Copyright (C) 2004-2007 Carlo de Falco
+ ##
+ ##
+ ##
+ ## SECS2D is free software; you can redistribute it and/or modify
+ ## it under the terms of the GNU General Public License as published by
+ ## the Free Software Foundation; either version 2 of the License, or
+ ## (at your option) any later version.
+ ##
+ ## SECS2D is distributed in the hope that it will be useful,
+ ## but WITHOUT ANY WARRANTY; without even the implied warranty of
+ ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ ## GNU General Public License for more details.
+ ##
+ ## You should have received a copy of the GNU General Public License
+ ## along with SECS2D; If not, see <http://www.gnu.org/licenses/>.
+
+ h=nodes(elements(:,2))-nodes(elements(:,1));
+
+ c=acoeff./h;
+ Bneg=Ubernoulli(-(v(2:Nnodes)-v(1:Nnodes-1))*bcoeff,1);
+ Bpos=Ubernoulli( (v(2:Nnodes)-v(1:Nnodes-1))*bcoeff,1);
+
+
+ d0 = [c(1).*Bneg(1); c(1:end-1).*Bpos(1:end-1)+c(2:end).*Bneg(2:end); c(end)*Bpos(end)];
+ d1 = [1000;-c.* Bpos];
+ dm1 = [-c.* Bneg;1000];
+
+ A = spdiags([dm1 d0 d1],-1:1,Nnodes,Nnodes);
+
+ % Last Revision:
+ % $Author: adb014 $
+ % $Date: 2008-02-04 16:26:27 +0100 (man, 04 feb 2008) $