Examples
The vector-valued function \(f\)
representing the system can be specified as a vector of
characters, or a function returning a numeric
vector, giving the values of the derivatives at time \(t\). The initial conditions are set with
the argument var and the time variable can be specified
with timevar.
Symbolic system
\[ \frac{dx}{dt}=x, \quad x_0 = 1 \]
f <- "x"
var <- c(x=1)
times <- seq(0, 2*pi, by=0.001)
x <- ode(f = f, var = var, times = times)
plot(times, x, type = "l")
Time dependent system
\[ \frac{dx}{dt}=\cos(t), \quad x_0 = 0 \]
f <- "cos(t)"
var <- c(x=0)
times <- seq(0, 2*pi, by=0.001)
x <- ode(f = f, var = var, times = times, timevar = "t")
plot(times, x, type = "l")
Multivariate system
\[ \frac{d}{dt} \begin{bmatrix} x\\ y \end{bmatrix}= \begin{bmatrix} x\\ x(1+\cos(10t)) \end{bmatrix}, \quad \begin{bmatrix} x_0\\y_0 \end{bmatrix}= \begin{bmatrix} 1\\1 \end{bmatrix} \]
f <- c("x", "x*(1+cos(10*t))")
var <- c(x=1, y=1)
times <- seq(0, 2*pi, by=0.001)
x <- ode(f = f, var = var, times = times, timevar = "t")
matplot(times, x, type = "l", lty = 1, col = 1:2)
Numerical system
\[ \frac{d}{dt} \begin{bmatrix} x\\ y \end{bmatrix}= \begin{bmatrix} x\\ y \end{bmatrix}, \quad \begin{bmatrix} x_0\\y_0 \end{bmatrix}= \begin{bmatrix} 1\\2 \end{bmatrix} \]
f <- function(x, y) c(x, y)
var <- c(x=1, y=2)
times <- seq(0, 2*pi, by=0.001)
x <- ode(f = f, var = var, times = times)
matplot(times, x, type = "l", lty = 1, col = 1:2)
Vectorized interface
\[ \frac{d}{dt} \begin{bmatrix} x\\ y\\ z \end{bmatrix}= \begin{bmatrix} x\\ y\\ y*(1+cos(10*t)) \end{bmatrix}, \quad \begin{bmatrix} x_0\\y_0\\z_0 \end{bmatrix}= \begin{bmatrix} 1\\2\\2 \end{bmatrix} \]
f <- function(x, t) c(x[1], x[2], x[2]*(1+cos(10*t)))
var <- c(1,2,2)
times <- seq(0, 2*pi, by=0.001)
x <- ode(f = f, var = var, times = times, timevar = "t")
matplot(times, x, type = "l", lty = 1, col = 1:3)