for kk=1:(n-1)
 for ii=(kk+1):n
	factor(ii,kk)=a(ii,kk)/a(kk,kk);
	for jj=kk:n
		a(ii,jj)=a(ii,jj)-factor(ii,kk)*a(kk,jj);
	end
	b(ii)=b(ii)-factor(ii,kk)*b(kk);
 end
end