inst/examples/PendulumRK4App.R

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

#
# PendulumRK4App.R
#

library(ggplot2)

source(paste(system.file("examples", package = "rODE"),
             "PendulumRK4.R",
             sep ="/"))

PendulumRK4App <- function(verbose = FALSE) {
    pendulum <- PendulumRK4()
    dt <- 0.1
    theta <- 0.2
    thetaDot <- 0
    pendulum@state[3] <- 0      # set time to zero, t = 0
    pendulum <- setState(pendulum, theta, thetaDot)
    pendulum <- setStepSize(pendulum, dt = dt) # using stepSize in RK4
    pendulum@odeSolver <- setStepSize(pendulum@odeSolver, dt) # set new step size
    rowvec <- vector("list")
    i <- 1
    while (getState(pendulum)[3] <= 20)    {
        rowvec[[i]] <- list(state1 = getState(pendulum)[1], # angle
                            state2 = getState(pendulum)[2],      # derivative of the angle
                            state3 = getState(pendulum)[3])       # time
        i <- i + 1
        pendulum <- step(pendulum)
    }
    return(data.table::rbindlist(rowvec))
}

solution <- PendulumRK4App()
plot(solution)