  DeGroot-style opinion formation presumes a continuous interaction among
agents of a social network. Hence, it cannot handle agents external to the
social network that interact only temporarily with the permanent ones. Many
real-world organisations and individuals fall into such a category. For
instance, a company tries to persuade as many as possible to buy its products
and, due to various constraints, can only exert its influence for a limited
amount of time. We propose a variant of the DeGroot model that allows an
external agent to interact with the permanent ones for a preset period of time.
We obtain several insights on maximising an external agent's influence in
opinion formation by analysing and simulating the variant.
