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tops
2011 Feb 15
0
Delta method using numerical derivatives
...ndly, Mark.
## numerically calculate the gradient (func may return a vector)
grad <- function(func,x,...) # would shadow numDeriv::grad()
{
h <- .Machine$double.eps^(1/3)*ifelse(abs(x)>1,abs(x),1)
temp <- x+h
h.hi <- temp-x
temp <- x-h
h.lo <- x-temp
twoeps <- h.hi+h.lo
nx <- length(x)
ny <- length(func(x,...))
if (ny==0L) stop("Length of function equals 0")
df <- if(ny==1L) rep(NA, nx) else matrix(NA, nrow=nx,ncol=ny)
for (i in 1L:nx) {
hi <- lo <- x
hi[i] <- x[i] + h.hi[i]
lo[i] &l...