Thanks for the correction! I also apologize for the garbled R output, due to copy-pasting formatted text from RStudio.
Tarmo On Fri, Mar 16, 2012 at 11:33 AM, mike_liz....@tiscali.co.uk < mike_liz....@tiscali.co.uk> wrote: > I think these probability distribution functions were > meant to be > instructive than indestructible. > > In the case of binomialprob, there > is indeed a problem > in binomialdist when p is quite small and n is > quite large. > A switch was used when p <: 0.5; it should instead > apply > when p>0.5 : > > binomialdist=: 3 : 0 > 'p n'=. y > if. b=. p>0.5 do. > p=. -. p end. NB. NOT p<:0.5 !!! > q=. -.p > r=. }.i.>:n > r=. (q^n)**/\1,(p% > q)*(>:n-r)%r > if. b do. |. r end. > ) > > binomialprob 0.0143281399120119, > 2872 41 41 > 0.0626089 > > Mike > > > On 15/03/2012 4:19 PM, Tarmo Veskioja > wrote: > > The syntax description is here: > > > http://www.jsoftware.com/jwiki/Addons/stats/base/distribution#binomialdist > > > > A simple working example: > > > > load 'statdist' > > binomialdist 0.5 5 > > > NB. 0.03125 0.15625 0.3125 0.3125 0.15625 0.03125 > > > > > binomialprob 0.5 5 4 4 NB. what are the odds of getting 4 successes > > > out of 5 trials with success of 0.5 in any individual trial > > NB. > 0.15625 > > > > The same in R or RStudio: > > > > dbinom(4, 5, 0.5)[1] 0.15625 > > > > > ------------------------------------ > > Now some unexpected results: > > > > > First in RStudio: > > > >> dbinom(41, 2872, 0.0143281399120119)[1] > 0.06260893 > > > > And now in j602a: > > binomialprob 0.0143281399120119 2872 > 41 41 > > NB. 0 > > > > x: binomialprob 0.0143281399120119 2872 41 41 > > NB. 0 > > > > > I also get weird results with this: > > binomialdist 0.07 280 > > > > And > this: > > binomialprob 0.075 280 20 20 > > NB. _ > > > > The last one in > RStudio gives this result: > > > >> dbinom(20, 280, 0.075)[1] 0.08980949 > > > -------------------- > > > > > > Is this a bug in j602a statdist package? > > > My Package Manager shows stats/distribs version as 1.0.2, which is > > > indicated as the latest. > > > > Regards, > > Tarmo Veskioja > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
