dfdt: Right Side of a first order ODE
In nlsrk: Runge-Kutta Solver for Function nls()

Description Usage Arguments Details Value Note Author(s) References See Also Examples

Gives the value of the right side of a first order Ordinary Differential Equation Used in frunge (Numeric resolution using Runge-Kutta 4 metthod)

1	dfdt(t, y, param)

`t`	time, independent variable
`y`	values of the unknown function at t
`param`	numeric vector : the set of parameters defining the function

the unique expression composing the body of dfdt is intended as the right side of the first order differential equation :

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.

a single float numeric value : the derivative of the unknown function at time t.

When used as argument for frunge, the initial condition y0 may be used as a parameter subject to fitting by nls, for instance. In this condition, y0 must appear as the last parameter in param and must not be used nor modified in dfdt

Jean-Sebastien Pierre
Jean-sebastien.pierre@univ-rennes1.fr

Any textbook in mathematics

frunge, nls

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## 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)