Fig. 9

a–c shows the spread of the infection in the model considered in “A simple network and epidemic model and a simple algorithm” section, which is equivalent to the growth of the RERT, with \(d=2\). Dark blue edges show the contacts on day t, and light blue edges show contacts present on previous days (and thus subfigures). Orange (resp., red; black) nodes mark symptomatic non-hospitalized (resp, asymptomatic; symptomatic hospitalized) nodes. d–f shows the LS source identification algorithm introduced in “Back of the envelope calculation” section, which finds the source in this example because there are no asymptomatic nodes on the transmission path between the first hospitalized node and the source. Black edges show the queried edges, and black stroke marks nodes already discovered by the algorithm. A node with black X marks a negative test result, and red stroked node marks the node currently maintained as source candidate by the LS algorithm