function [ x ] = bs(A)
[r c]=size(A);
x=zeros(r,1);
for j=1:r
    y(c-j,1)=A(c-j,r+1);
    for k= c+1-j:r
        y(c-j,1)=y(c-j,1)-A(c-j,k)*x(k,1);
    end
    x(c-j,1)=y(c-j,1)/A(c-j,c-j);
end
end

