function A=em(B)
[m,n]=size(B);
for i=1:m-1
    C=B(i:m,i:i);
    [u,l,v]=find(C);
    k=u(1);
    B(([i+k-1,i]),:)=B(([i,i+k-1]),:);
    E=B(i:i,i+1:n);
    [x,y,z]=find(E);
    g=length(u);
    h=length(y); 
        for w=1:h
        for l=2:g
            B(i+u(l)-1,i+y(w))=mod(B(i+u(l)-1,i+y(w))+1,2);
        end;
        end;
    B=gf2gauss(B,i,i);
    times=i
end,B;
A=B;