D1=semivariance(DATA)

function D1=semivariance(DATA)
%the variable h1 can be changed to your interest
%if you don't change h1,the time series should be of length greater than 2500
%code by Guan Wenye,[e-mail]
h1=100:200:2000;
h1=h1';
N1=length(h1);
rh=zeros(N1,1);
n=1;
    for t1=100:200:2000
        rh1=sum((DATA(1:t1)-DATA((1+t1):(2*t1))).^2);
       rh(n)=rh1/2/t1;
       n=n+1;
    end
    plot(log(h1),log(rh),'*')
    hold on
     h2=polyfit(log(h1),log(rh),1);
     plot([log(h1(1)) log(h1(N1))],[polyval(h2,log(h1(1)))  polyval(h2,log(h1(N1)))],'r')
     D1=(4-h2(1))/2;