Sub LUBKSB(A(), N, INDX(), B())
    II = 0
    For I = 1 To N
        LL = INDX(I)
        Sum = B(LL)
        B(LL) = B(I)
        If II <> 0 Then
            For J = II To I - 1
                Sum = Sum - A(I, J) * B(J)
            Next J
        ElseIf Sum <> 0# Then
            II = I
        End If
        B(I) = Sum
    Next I
    For I = N To 1 Step -1
        Sum = B(I)
        If I < N Then
            For J = I + 1 To N
                Sum = Sum - A(I, J) * B(J)
            Next J
        End If
        B(I) = Sum / A(I, I)
    Next I
End Sub