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function outIndex = systematicR(inIndex,wn); 
% PURPOSE : Performs the resampling stage of the SIR 
%           in order(number of samples) steps. It uses the 
%           systematic sampling scheme of Carpenter and Clifford. 
% INPUTS  : - inIndex = Input particle indices. 
%           - wn = Normalised importance ratios. 
% OUTPUTS : - outIndex = Resampled indices. 
% AUTHORS  : Arnaud Doucet and Nando de Freitas - Thanks for the acknowledgement. 
% DATE     : 08-09-98 
 
if nargin < 2, error('Not enough input arguments.'); end 
 
wn=wn'; 
[arb,N] = size(wn);  % N = Number of particles. 
 
% SYSTEMATIC RESAMPLING: 
% ==================== 
 
N_children=zeros(1,N); 
label=zeros(1,N); 
label=1:1:N; 
 
s=1/N; 
auxw=0; 
auxl=0; 
li=0;   % Label of the current point 
% Initialisation 
T=s*rand(1); 
j=1; 
Q=0; 
i=0; 
 
% Sampling before 
u=rand(1,N); 
while (T<1) 
   if (Q>T) 
      T=T+s; 
      N_children(1,li)=N_children(1,li)+1; 
   else 
      % select i uniformly between j and N 
      i=fix((N-j+1)*u(1,j))+j; 
      % save the associate characteristic 
      auxw=wn(1,i); 
      li=label(1,i); 
      % update the cfd 
      Q=Q+auxw; 
      % swap  
      wn(1,i)=wn(1,j); 
      label(1,i)=label(1,j); 
      %wn(1,j)=auxw; 
      %label(1,j)=li; 
      j=j+1; 
   end 
end 
 
% COPY RESAMPLED TRAJECTORIES:   
% ============================ 
index=1; 
for i=1:N 
  if (N_children(1,i)>0) 
    for j=index:index+N_children(1,i)-1 
      outIndex(j) = inIndex(i); 
    end; 
  end;    
  index= index+N_children(1,i);    
end