Gives the value of the right side of a first order Ordinary Differential Equation
Used in frunge (Numeric resolution using Runge-Kutta 4 metthod)
Usage
dfdt(t, y, param)
Arguments
t
time, independent variable
y
values of the unknown function at t
param
numeric vector : the set of parameters defining the function
Value
a single float numeric value : the derivative of the unknown function at time t.
Details
the unique expression composing the body of dfdt is intended as the right side of the first order
differential equation :
$$ \frac{dy}{dt} = dfdt(t,y,param)$$
The function body has to be written by the user.
param must take the form c(param1,param2,param3).
if the initial value (y0) is used as a parameter (for model fitting for instance), it must be the last
in the list and not used in dfdt.
## Solves and draws the logistic function using default dfdt as provided in the package frunge(t=10, param=c(r=0.1,k=100), y0=3, Dfdt = dfdt, dt = 0.01, graph = TRUE)