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):                                        
%       2000-2001 by Forschungszentrum Telekommunikation Wien, Austria;
%                                                         All rights reserved.
% Project       : FSAN xDSL simulation tool
% Author(s)     : Tomas Nordstrom (Tomas.Nordstrom@FTW.at)
%
% CVS:       $Id: getZin.m,v 1.2 2001/12/18 09:44:45 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
%% ===========================================================================

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});

% 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});