setStepSize

setStepSize uses either of two step parameters: stepSize and dt stepSize works for most of the applications dt is used in Pendulum

setStepSize(object, ...)

Arguments

object	a class object
...	additional parameters

Examples

# ++++++++++++++++++++++++++++++++++++++++++++++++++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()
#> Found more than one class "RK4" in cache; using the first, from namespace 'rODE'
#> Also defined by ‘.GlobalEnv’
plot(solution)
# ++++++++++++++++++++++++++++++++++++++++++++++++  example: ComparisonRK45App.R
# Compares the solution by the RK45 ODE solver versus the analytical solution
# Example file: ComparisonRK45App.R
# ODE Solver:   Runge-Kutta 45
# ODE class :   RK45
# Base class:   ODETest

importFromExamples("ODETest.R")

 ComparisonRK45App <- function(verbose = FALSE) {
     ode <- new("ODETest")                     # create an `ODETest` object
     ode_solver <- RK45(ode)                   # select the ODE solver
     ode_solver <- setStepSize(ode_solver, 1)      # set the step

     # Two ways of setting the tolerance
       # ode_solver <- setTolerance(ode_solver, 1e-8)  # set the tolerance
     setTolerance(ode_solver) <-  1e-8

     time <-  0
     rowVector <- vector("list")
     i <- 1
     while (time < 50) {
         rowVector[[i]] <- list(t  = getState(ode)[2],
                                s1 = getState(ode)[1],
                                s2 = getState(ode)[2],
                                xs = getExactSolution(ode, time),
                                counts = getRateCounts(ode),
                                time   = time
                                )
         ode_solver <- step(ode_solver)           # advance one step
         stepSize   <- getStepSize(ode_solver)
         time <- time + stepSize
         ode  <- getODE(ode_solver)                     # get updated ODE object
         i <- i + 1
     }
     return(data.table::rbindlist(rowVector))    # a data table with the results
 }
# show solution
solution <- ComparisonRK45App()                          # run the example
plot(solution)