function x=felso(A,b)
  [n,m]=size(A)
  x=zeros(m,1)
  x(n)=b(n)/A(n,n)
  for i=n-1:-1:1
    x(i)=(b(i)-A(i,i+1:m)*x(i+1:m))/A(i,i)
  endfor
endfunction