Proof of Theorem 3.3
Theorem 3.3. Suppose that has a multivariate Taylor expansion with a positive definite Hessian at
. Then we have
.
Proof: Given there exists
such that
with being the Hessian with respect to
and
. Considering the positive definiteness of the Hessian at the stationary point
and the smoothness of
, we know that if
, then
implies that
for some
.
Since is a bounded sequence, there is a subsequence
such that
as
. For every
, choosing
such that
, we can take
large enough such that
. Recalling the above paragraph, we have
. By taking
, we have
which implies
. At this stage, the conclusion obviously holds true.
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