inst/shiny-examples/rosenzweig.R

In deBif: Bifurcation Analysis of Ordinary Differential Equation Systems

# The Rosenzweig-McArthur predator-prey model
# -------------------------------------------

# Equations:
# ----------
#
# dR            R       R
# -- = r R (1 - -) - ------- C
# dt            K    1 + ahR
#
# dC          R
# -- = eps -------C - mu C
# dt       1 + ahR
#

# The initial state of the system has to be specified as a named vector of state values.
RMstate <- c(R = 0.05, C = 0.1)

# Parameters have to be specified as a named vector of parameters.
RMparms <- c(r = 0.5, K = 0.1, a = 5.0, h = 3.0, eps = 0.5, mu = 0.05)

# The model has to be specified as a function that returns
# the derivatives as a list. You can adapt the body below
# to represent your model
rosenzweig <- function(t, state, parms) {
  with(as.list(c(state,parms)), {

    dR = r*R*(1 - R/K) - a*R*C/(1 + a*h*R)
    dC = eps*a*R*C/(1 + a*h*R) - mu*C

    # The order of the derivatives in the returned list has to be
    # identical to the order of the state variables contained in 
    # the argument `state`
    return(list(c(dR, dC)))
  })
}

bifurcation(rosenzweig, RMstate, RMparms)