// determine the next event
func (w *WFPopulation) nextEvent() (eventType int, eventTime float64) {
k := float64(len(w.history.CurrentPool))
p := 2.0 * w.TransferRate * float64(w.Size)
l := (k*p + k*(k-1.0)) / 2.0
v := randist.ExponentialRandomFloat64(w.rng, 1.0/l)
eventTime = v
r := randist.UniformRandomFloat64(w.rng)
if r < p/(k-1.0+p) {
eventType = TransferEvent
} else {
eventType = CoalescenceEvent
}
return
}
// evolutionary operators: mutation and transfer
func (pop *SeqPop) manipulate() {
// calculate the number of events, which is poisson distribution
lambda := float64(pop.Size) * float64(pop.Length) * (pop.Mutation + pop.Transfer)
if pop.ExpTime {
t := randist.ExponentialRandomFloat64(pop.rng, 1.0)
lambda = t * lambda
}
k := randist.PoissonRandomInt(pop.rng, lambda)
// given k, the number of mutations or transfers are following Binormial distribution.
// therefore, we can do k times of Bernoulli test
for i := 0; i < k; i++ {
// determine whether this event is a mutation or transfer
ratio := pop.Mutation / (pop.Mutation + pop.Transfer) // the ratio of mutation
r := randist.UniformRandomFloat64(pop.rng) // randomly produce a probability
if r <= ratio { // determin whether is a mutation or transfer
pop.mutate()
} else {
pop.transfer()
}
}
}