getEnergy-method: getEnergy

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

Description

Get the calculated energy level

Usage

getEnergy(object, ...)

Arguments

object	a class object
...	additional parameters

Examples

# KeplerEnergy.R
#

setClass("KeplerEnergy", slots = c(
    GM        = "numeric",
    odeSolver = "Verlet",
    counter   = "numeric"
    ),
    contains = c("ODE")
)

setMethod("initialize", "KeplerEnergy", function(.Object, ...) {
    .Object@GM <- 4 * pi * pi         # gravitation constant times combined mass
    .Object@state <- vector("numeric", 5)  # x, vx, y, vy, t
    # .Object@odeSolver <- Verlet(ode = .Object)
    .Object@odeSolver <- Verlet(.Object)
    .Object@counter <- 0
    return(.Object)
})

setMethod("doStep", "KeplerEnergy", function(object, ...) {
    object@odeSolver <- step(object@odeSolver)
    object@state <- object@odeSolver@ode@state
    object
})

setMethod("getTime", "KeplerEnergy", function(object, ...) {
    return(object@state[5])
})

setMethod("getEnergy", "KeplerEnergy", function(object, ...) {
    ke <- 0.5 * (object@state[2] * object@state[2] +
                     object@state[4] * object@state[4])
    pe <- -object@GM / sqrt(object@state[1] * object@state[1] +
                                object@state[3] * object@state[3])
    return(pe+ke)
})


setMethod("init", "KeplerEnergy", function(object, initState, ...) {
    object@state <- initState
    object@odeSolver <- init(object@odeSolver, getStepSize(object@odeSolver))
    object@counter <- 0
    object
})


setReplaceMethod("init", "KeplerEnergy", function(object, ..., value) {
    initState <- value
    object@state <- initState
    object@odeSolver <- init(object@odeSolver, getStepSize(object@odeSolver))
    object@counter <- 0
    object
})

setMethod("getRate", "KeplerEnergy", function(object, state, ...) {
    # Computes the rate using the given state.
    r2 <- state[1] * state[1] + state[3] * state[3]  # distance squared
    r3 <- r2 * sqrt(r2)   # distance cubed
    object@rate[1] <- state[2]
    object@rate[2] <- (- object@GM * state[1]) / r3
    object@rate[3] <- state[4]
    object@rate[4] <- (- object@GM * state[3]) / r3
    object@rate[5] <- 1   # time derivative

    object@counter <- object@counter + 1
    object@rate

})


setMethod("getState", "KeplerEnergy", function(object, ...) {
    # Gets the state variables.
    return(object@state)
})

# constructor
KeplerEnergy <- function() {
    kepler <- new("KeplerEnergy")
    return(kepler)
}

f0nzie/rODE documentation built on May 14, 2019, 10:34 a.m.