Definition 4. External Influence Component: In disease transmission, the imported
cases from foreign or distant endemic countries and regions are another major factor
that can cause local epidemics . Thus, we consider this factor in the disease
transmission network as an external node connected to all the other nodes. In G, this
is denoted as an edge e0i from external node to node i with weight w0i.
Xiaofei Yang. Inferring disease transmission networks at a metapopulation level. (2014)
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