[R] Deriving formula with deriv

From: kitty <kitty.a1000_at_gmail.com>
Date: Mon, 04 Apr 2011 11:35:08 +0100

Dear list,


I am trying to get the second derivative of a logistic formula, in R summary the model is given as :

>Nonlinear regression model

  >model: data ~ logistic(time, A, mu, lambda, addpar)    >data: parent.frame()
     > A mu lambda
>0.53243 0.03741 6.94296


but I know the formula used is

# y~'A'/(1+exp((4*'mu'/'A')*('lambda'-'time'))+2)) # from the grofit ( package I am using to fit the model) documentation.

I have attempted to use the R function 'deriv' to get the first derivative from which I can then reuse the deriv function to get the second derivative.... unfortunately this does not seem to work

> express

expression(y ~ "A"/(1 + exp((4 * "mu"/"A") * ("lambda" - "time")) +


> d1<-deriv(express)

Error in deriv.default(express) : element 2 is empty;

   the part of the args list of '.Internal' being evaluated was:    (expr, namevec, function.arg, tag, hessian)  ####

Why is this not working and how do I get the second derivative?

Thank you for reading my post, all help is appreciated, Kitty

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