function ex=countEX(x);
%計算樣本矩陣x的ex值作為判斷類內離散度的依據

xm=(mean(x))'; 
[r,c]=size(x);
exa=zeros(1,r);
tt=0;
for i=1:r
    temp=(x(i,:))'-xm;
    for j=1:c
        tt=tt+temp(j,:)^2;
    end
    exa(1,i)=tt;
end
 ex=mean(exa);