function [flag]=disptrell(dlt,slt,data_est,state_est,varargin)

%**************************************************************************
%DISPTRELL Display decoding process in graphical form.
%   DISPTRELL(DLT,SLT,D_E,S_E) displays most probable path and data
%   estimations in decoding process. DLT and SLT look-up tables are
%   required to display code trellis with all possible transitions. The
%   DISPTRELL function doesn't affect the detection process. It's just a
%   tool intended for lectures and presentations. As it belongs to the
%   Visual Layer it's not included in the VITERBI function to speed up
%   decoding process.
%**************************************************************************

flag=0;

[s,md,space_dim] = size(dlt);
[symbols,foo,frames] = size(data_est);
framecut = 15;

% only one frame perfigure can be displayed
if frames > 1
  data_est = data_est(:,1,1);
end

% max 20 symbols can be displayed
if symbols > 20
    flag=1;
  endstate = framecut;
  data_est = data_est(1:framecut,1,1);
else
  endstate = symbols;
end

% default shrink factor
if length(varargin) == 1
  shrink = varargin{1};
else
  shrink = 1 / 2;
  shrink_axis = (s + 1) * shrink;
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% BODY BEGIN %%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

offset = 0.1;
figure;
clf;

for k = 1:endstate
  x1 = k; x2 = k + 1;
  for i = 1:s
    for j = 1:md
      y1 = i;
      y2 = slt(i,j,:);
      trellis = line([x1 x2],[y1,y2]);
      set(trellis,'LineStyle',':');
    end
    str = num2str(i);
    text(0.5,i,str,'HorizontalAlignment','Center');
  end
  backpath = line([k k + 1],[state_est(k) state_est(k + 1)]);
  set(backpath,'Color','red','LineWidth',2);
  str1 = num2str(k);
  text(k + 1,s + 1,str1,'HorizontalAlignment','Center');
  
  str2 = num2str(data_est(k));
  str3 = text(k + offset,state_est(k) - offset,str2);
  set(str3,'HorizontalAlignment','Center','FontWeight','bold');
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% BODY END %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

text((endstate + 1) / 2,s + 2,'Steps [\itk\rm]')
h=text(4,-0.5,'States: Only one packet displayed','HorizontalAlignment','Center');
set(h,'FontWeight','bold','FontSize',12,'Color','b');

legend([backpath;trellis],['Back path  ';'Transitions']);

figtitle = ['Best path found with Viterbi iterative decoder'];
wintitle = [figtitle];
ft = title(figtitle);

set(ft,'FontWeight','bold','FontSize',12,'Color','r');
set(gcf,'Name',wintitle);
set(gcf,'NumberTitle','off');


axis([1,endstate + 1,1 - (s / shrink_axis),s + (s / shrink_axis)]);
axis off;
view(0,-90);