(i) if H is a positive definite matrix and kH
−1
k
gkk < △, then for the solution of d
∗ of (QP), kd
kk = △
does note hold; i.e., in this case the solution of (QP) does not lie on the boundary of the feasible set.
Assume that Hk is a positive definite, kH
−1
k
gk < △ and kd
kk = △ hold at the same time. Hence,
from Thm. 4.6.2(b), we have that