inst/examples/SpringRK4App.R

In f0nzie/rODE: Ordinary Differential Equation (ODE) Solvers Written in R Using S4 Classes

# ++++++++++++++++++++++++++++++++++++++++++++++++++application:  SpringRK4App.R
# Simulation of a spring considering no friction

importFromExamples("SpringRK4.R")


# run application
SpringRK4App <- function(verbose = FALSE) {
    theta    <- 0
    thetaDot <- -0.2
    tmax     <- 22; dt <- 0.1
    spring <- SpringRK4()
    spring@state[3] <- 0      # set time to zero, t = 0
    spring <- setState(spring, theta, thetaDot)
    #  spring <- setStepSize(spring, dt = dt) # using stepSize in RK4
    spring@odeSolver <- setStepSize(spring@odeSolver, dt) # set new step size
    rowvec <- vector("list")
    i <- 1
    while (getState(spring)[3] <= tmax)    {
        rowvec[[i]] <- list(t  = getState(spring)[3],      # angle
                            y1 = getState(spring)[1],      # derivative of the angle
                            y2 = getState(spring)[2])      # time
        i <- i + 1
        spring <- step(spring)
    }
    DT <- data.table::rbindlist(rowvec)
    return(DT)
}

# show solution
solution <- SpringRK4App()
plot(solution)