Central difference numerical gradient approximation.

grcentral computes the central difference approximation to the gradient of user function userfn.

grcentral(par, userfn, fbase=NULL, env=optsp, ...)

Arguments

par: parameters to the user objective function userfn
userfn: User-supplied objective function
fbase: The value of the function at the parameters, else NULL. This is to save recomputing the function at this point.
env: Environment for scratchpad items (like deps for approximation control in this routine). Default optsp.
...: optional arguments passed to the objective function.

Details

Package:	grcentral
Depends:	R (>= 2.6.1)
License:	GPL Version 2.

Value

grcentral returns a single vector object df which approximates the gradient of userfn at the parameters par. The approximation is controlled by a global value optderiveps that is set when the package is attached.

Author

John C. Nash

Examples

cat("Example of use of grcentral\n")
#> Example of use of grcentral

myfn<-function(xx, shift=100){
    ii<-1:length(xx)
    result<-shift+sum(xx^ii)
}
xx<-c(1,2,3,4)
ii<-1:length(xx)
print(xx)
#> [1] 1 2 3 4
gn<-grcentral(xx,myfn, shift=0)
print(gn)
#> [1]   1   4  27 256
ga<-ii*xx^(ii-1)
cat("compare to\n")
#> compare to
print(ga)
#> [1]   1   4  27 256