where formula_101 are real numbers, and formula_102 is a positive real number. The flexibility of the curve formula_9 is due to the parameter formula_102: (i) if formula_105 then the curve reduces to the logistic function, and (ii) if formula_102 converges to zero, then the curve converges to the Gompertz function. In epidemiological modeling, formula_107, formula_108, and formula_109 represent the final epidemic size, infection rate, and lag phase, respectively. See the right panel for an examplary infection trajectory when formula_110 are designated by formula_111.