lotka-volterra.R

# source: https://www.r-bloggers.com/lotka-volterra-model%C2%A0%C2%A0intro/
library(deSolve)

LotVmod <- function (Time, State, Pars) {
  with(as.list(c(State, Pars)), {
    dx = x * (alpha - beta * y)
    dy = -y * (gamma - delta * x)
    return(list(c(dx, dy)))
  })
}

Pars <- c(alpha = 2, beta = .5, gamma = .2, delta = .6)
State <- c(x = 10, y = 10)
Time <- seq(0, 100, by = 1)

out <- as.data.frame(ode(func = LotVmod, y = State, parms = Pars, times = Time))

matplot(out[,-1], type = "l", xlab = "time", ylab = "population")
legend(
  "topright", 
  c("Cute bunnies", "Rabid foxes"), 
  lty = c(1,2), col = c(1,2), box.lwd = 0
)