R help - Dec 2002 - Partial Sums

Is it possible to calculate partial sums in R?

I have the equation:

Px  =  (k / x) * SUM_{from j >= x to infinity} Pj             x=1,2,3,...

where k is a parameter, Pj is the Poisson probability, and x is a rank.
(This is for rank-frequency data.)  In other words, the frequency of an
entity at rank x depends on the sum of frequencies of all entities at
ranks j > x.

Many thanks,
Andrew Wilson

Dr Andrew Wilson <eia018 at comp.lancs.ac.uk> writes:
> Is it possible to calculate partial sums in R?
> 
> I have the equation:
> 
> Px  =  (k / x) * SUM_{from j >= x to infinity} Pj            
x=1,2,3,...
> 
> where k is a parameter, Pj is the Poisson probability, and x is a rank.
> (This is for rank-frequency data.)  In other words, the frequency of an
> entity at rank x depends on the sum of frequencies of all entities at
> ranks j > x.
With some restriction on k and the Poisson intensity lambda, I presume?

How about

  k/x * (1-ppois(x-1,lambda))

or am I overlooking something??

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907