how to find largest Lyapunov exponent for Lorenz in Rosenstein's Algorithm?

function d = lyarosenstein(x,f,m,tao,meanperiod,maxiter) 
% d:divergence of nearest trajectoires
% x:signal
% tao:time delay
% m:embedding dimension

N=length(x);


% [T, X] = feval(@ode45, @rossler, [1 100 + .01], x);
M=N-(m-1)*tao;
Y=psr_deneme(x,m,tao);
for i=1:M
    
    x0=ones(M,1)*Y(i,:);
    distance=sqrt(sum((Y-x0).^2,2));
    for j=1:M
        if abs(j-i)<=meanperiod
            distance(j)=1e10;
        end
    end
    [neardis(i) nearpos(i)]=min(distance);
end
for k=1:maxiter
    
    maxind=M-k;
    evolve=0;
    pnt=0;
    for j=1:M
        if j<=maxind && nearpos(j)<=maxind
            dist_k=sqrt(sum((Y(j+k,:)-Y(nearpos(j)+k,:)).^2,2));
             if dist_k~=0
                evolve=evolve+log(dist_k);
                pnt=pnt+1;
             end
        end
    end
    if pnt > 0
        d(k)=evolve/pnt;
    else
        d(k)=0;
    end
    
end
figure
plot(log(d))
% LLE Calculation
fs=2000;%sampling frequency
tlinear=15:78;
F = polyfit(tlinear,d(tlinear),1);
lle = F(1)*fs;

function Y=psr_deneme(x,m,tao,npoint)
%Phase space reconstruction
%x : time series 
%m : embedding dimension
%tao : time delay
%npoint : total number of reconstructed vectors
%Y : M x m matrix
% author:"Merve Kizilkaya"
N=length(x);
if nargin == 4
    M=npoint;
else
    M=N-(m-1)*tao;
end
Y=zeros(M,m); 
for i=1:m
    Y(:,i)=x((1:M)+(i-1)*tao)';
end
%