inst/examples/Reaction.R

In rODE: Ordinary Differential Equation (ODE) Solvers Written in R Using S4 Classes

# Reaction.R

# /**
# * Reaction models an autocatalytic oscillating chemical reaction
# * (Brusselator model) by implementing the ODE interface.
# * @author Wolfgang Christian
# * @version 1.0
# * Converted to R by: Alfonso R. Reyes
#
# */


setClass("Reaction", slots = c(
    k1 = "numeric",
    k2 = "numeric",
    k3 = "numeric",
    k4 = "numeric",
    A  = "numeric",
    B  = "numeric",
    state     = "numeric",
    odeSolver = "RK4"
    ),
    prototype = prototype(
        k1 = 1.0, k2 = 2.5, k3 = 1.0, k4 = 1.0,      # reaction rates
        A = 1, B = 1,                                # reactant concenterations
        state = c(0, 0, 0)      # X, Y, t
    ),
    contains = c("ODE")
    )


setMethod("getState", "Reaction", function(object) {
    object@state
})


setMethod("getRate", "Reaction", function(object, state, ...) {
    xxy <- state[1] * state[1] *state[2]
    object@rate[1] <- object@k1 * object@A - object@k2 * object@B * state[1] +
        object@k3 * xxy - object@k4 * state[1]                          # X rate
    object@rate[2] <- object@k2 * object@B * state[1] - object@k3 * xxy # Y rate
    object@rate[3] <- 1                       # rate of change of time, dt/dt

    object@rate                                                # time derivative
})


# constructor
Reaction <- function(initialConditions) {
    .Reaction <- new("Reaction")
    .Reaction@state <- initialConditions
    .Reaction
}