[R] obtaining output from an evaluated expression

[Jack Bowden]

Hi

I am trying to use the deriv and eval functions to obtain the value of a 
function , say  "xi-(alpha0+alpha1*gi)" , differentiated with respect to 
alpha0 and alpha1, in the following way

# for gi = 0

 > dU1dtheta  <- deriv(~ xi-(alpha0+alpha1*gi), c("alpha0","alpha1")) 
 > eval(dU1dtheta)
(Intercept) 
 -0.2547153 
attr(,"gradient")
     alpha0 alpha1
[1,]     -1      0

I want to extract the output gradient values of -1 and 0 but I don't 
know how to access them. The only thing I can access is the intercept  
term via.

 > eval(dU1dtheta)[1].

I'm sorry if this is too basic a question for the list, but any help 
would be greatly appreciated

Jack

-- 
Dr Jack Bowden
MRC Biostatistics Unit
Institute of Public Health
Forvie Site
Robinson Way
Cambridge
CB2 0SR

Tel: (01223) 330385