[R] How can we make a vector call a function element-wise efficiently?

[Eik Vettorazzi]

Hi ZhaoXing,
without knowledge about the ultimate purpose of your calculations its
quite difficult to give further hints.

best regards

Am 11.02.2011 14:35, schrieb zhaoxing731:
> Dear Eik
>  
> What a great idea!!! Thank you so much for your colossal improvment
> Yes, you have a unique eye on the numerical problem, I am worrying about
> this problem right now, hope you could give me new idea again
>  
> Hi,
> you compute the same results for logx many times. So it is easier and
> time saving tabulating all intermediate results.
> smth. like
>  n<-100000
>  CT=6000 #assignment to CT
>  NT=29535210 #assignment to NT
>  i <- 0:(n-1)
>  lookup<- lchoose(NT-n, CT-i) + lchoose(n, i)
>  lgmax<-cummax(lookup)
>  calsta2<-function(c) lgmax[c] + log(sum(exp(lookup[1:c] - lgmax[c])))
> should help for a start, but I think, you are running into numerical
> troubles, since you are dealing with very high and low (on log scale)
> numbers and calsta constantly returns 57003.6 for c>38 (the summands in
> sum(exp(logx - logmax)) will become 0 for c>38).
> #check
> sapply(1:50,calsta2)
> sapply(1:50,calsta)
> hth
> /Yours sincerely/
> / /
> ------------------------------------------------------------------------
> /ZhaoXing
> Department of Health Statistics
> West China School of Public Health
> Sichuan University
> No.17 Section 3, South Renmin Road
> Chengdu, Sichuan 610041
> P.R.China/


-- 
Eik Vettorazzi
Institut für Medizinische Biometrie und Epidemiologie
Universitätsklinikum Hamburg-Eppendorf

Martinistr. 52
20246 Hamburg

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