function [fi_tot] = getABCD(ex,start,stop,topology,f,Zterm);
%getABCD - Get the ABCD parameters
%          between start and stop node in the topology
%
% Parameter:    ex         experiment struct
% Parameter:    start      start node
% Parameter:    stop       stop node
% Parameter:    topology   Scenario Topology
% Parameter:    f	   Frequency axis
% Parameter:    Zterm      Termination Impedance
% Returns:      fi         The ABCD parameters
%                          A=fi_tot{1,1};  
%                          B=fi_tot{1,2};  
%                          C=fi_tot{2,1};  
%                          D=fi_tot{2,2};  
%
% Example(s):
%   segs = size(ex.tt.topology);
%   f = ex.param.frequency.f;
%   fi_tot = getABCD(ex,1,segs(1),ex.tt.topology,f,ex.param.Zterm);
%   Zl = ex.param.Zterm;
%   Zin = (fi_tot{1,1}.*Zl+fi_tot{1,2})./(fi_tot{2,1}.*Zl+fi_tot{2,2});
%
% Reference:
%    FSAN xDSL simulation tool manual
%% ===========================================================================

%% ===========================================================================
% Copyright (C):                                        
%       1999 by Telia Research AB, Lulea, Sweden;                
%       2000-2001 by Forschungszentrum Telekommunikation Wien, Austria;
%                                                         All rights reserved.
% Project       : FSAN xDSL simulation tool
% Author(s)     : Tomas Nordstrom (Tomas.Nordstrom@FTW.at)
%               : Daniel Bengtsson (Daniel.J.Bengtsson@Telia.se)
%
% CVS:       $Id: getABCD.m,v 1.4 2001/12/05 15:01:14 tono Exp $
%% ===========================================================================
% Change History
%      1999-08-11 (DaB)  Created
%      2000-03-14 (ToNo) Modified how cables are defined (now in a list)
%      2000-04-03 (UvAn) Changed according to new interface of getTwoPortModel
%      2000-07-05 (GS)   Modified for also accepting bridged tap directly at LT
%      2000-07-17 (ToNo) Split out ABCD calcs to its own function
%                        (Makes it easier to do calc things like Zin)    
%      2001-01-04 (InJo) Fixed bug in index start (added +1)
%      2001-02-22 (ToNo) Added support for insertion loss numbers
%                        Useful for splitters and cable models
%                        given as an IL number
%% ===========================================================================

temp=size(topology);

% Start with unity matrix
fi_tot{1,1}=1;
fi_tot{1,2}=0;
fi_tot{2,1}=0;
fi_tot{2,2}=1;

for index=start+1:stop,
    seg=topology(index,:);   
    temp=size(seg);
    cablename=seg{2};
    if ~isempty(cablename),
        % Take care of a cable section
        cablemodel = getList(ex.clist,cablename);
        switch cablemodel.model
         case 'IL'
          d=seg{1}./1000;
          fi{1,1}=1;
          fi{1,2}=getBFromIL(cablemodel,f,Zterm,d);
          fi{2,1}=0;
          fi{2,2}=1;
          fi_tot=ABCDprod(fi_tot,fi);  
         otherwise
          [Z0,gamma] = getTwoPortModel(cablemodel,f);
          d=seg{1}./1000;
          fi{1,1}=cosh(gamma*d);
          fi{1,2}=Z0.*sinh(gamma*d);
          fi{2,1}=1./Z0.*sinh(gamma*d);
          fi{2,2}=cosh(gamma*d);
          fi_tot=ABCDprod(fi_tot,fi);
        end;
    end
    
    if length(seg)>5,
        cablename=seg{6};
    else
        cablename='';
    end
    
    if ~isempty(cablename),
        % Take care of a bridge tap (with open circuit termination)
        d=seg{5}./1000;
        cablemodel = getList(ex.clist,cablename);
        [Z0,gamma] = getTwoPortModel(cablemodel,f);
        fi{1,1}=1;
        fi{1,2}=0;
        fi{2,1}=1./Z0.*tanh(gamma*d);
        fi{2,2}=1;
        fi_tot=ABCDprod(fi_tot,fi);
    end;
    
end;