function [Zin, ZinNT] = getZin(ex,start,stop,topology,f,Zterm);
%getZin - Get the input impedance
%         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:      Zin        Input impedance
%
% Example(s):
%   segs = size(ex.tt.topology);
%   f = ex.param.frequency.f;
%   Zin = getZin(ex,1,segs(1),ex.tt.topology,f,ex.param.Zterm);
%   semilogx(f,Zin); 
%
% Reference:
%    Chen "DSL simulations Techniques and Standards Development", 1998    
%% ===========================================================================

%% ===========================================================================
% Copyright (C):                                        
%       2000-2003 by Forschungszentrum Telekommunikation Wien, Austria;
%                                                         All rights reserved.
% Project       : FTW's xDSLsimu
% Author(s)     : Tomas Nordstrom (Tomas.Nordstrom@FTW.at)
%               : Daniel Bengtsson (Daniel.J.Bengtsson@Telia.se)
%		: Petr Kadlec (kadlec@ftw.at)
%
% CVS:       $Id: getZin.m,v 3.2 2003/11/03 12:33:22 tono Exp $
%% ===========================================================================
% Change History
%      2000-07-17 (ToNo) Split out a function getABCD to be able to do this
%      2001-12-17 (ToNo) Fixed a reverse impedance
%      2002-07-22 (PeKa) Octave port
%      2003-11-03 (ToNo) Lists now use cell arrays for both Octave and Matlab
%% ===========================================================================
Zl = Zterm; Zs = Zterm;
fi_tot = getABCD(ex,start,stop,topology,f,Zterm);

% From Starr Eq. 3.7 (or Chen p.48)
% Zin   =  (fi_tot{1,1}.*Zl+fi_tot{1,2})./(fi_tot{2,1}.*Zl+fi_tot{2,2});

Zin   =  (fi_tot{1}.*Zl+fi_tot{2})./(fi_tot{3}.*Zl+fi_tot{4});

% We can also calculate the reverse impedance (Chen p.53)
% ZinNT  = (fi_tot{2,2}.*Zs+fi_tot{1,2})./(fi_tot{2,1}.*Zs+fi_tot{1,1});

ZinNT  = (fi_tot{4}.*Zs+fi_tot{2})./(fi_tot{3}.*Zs+fi_tot{1});