If Pascals triangle is used for (i.! <:) , a considerable improvement can be
achieved:
Bn1=:[:{. (({.,[:+/ */),:(0&,+ ,&0)@{:)^:(]`(,:[EMAIL PROTECTED]:@1:))
(Bn-:Bn1 )120
1
5 ts'Bn 120'
0.32217713 140928
5 ts'Bn1 120'
0.02378813 167424
more than 10 times as efficient.
R.E. Boss
> -----Oorspronkelijk bericht-----
> Van: R.E. Boss [mailto:[EMAIL PROTECTED]
> Verzonden: maandag 17 december 2007 22:20
> Aan: 'Programming forum'
> Onderwerp: RE: [Jprogramming] Bell numbers
>
> Better performance gives the recursive formula from
> http://en.wikipedia.org/wiki/Bell_number
>
> Bn=: (, [:+/ (i.! <:)@# *])^:(]`(x:@1:))
>
> 5 ts 'bellN0X i.120'
> 0.47826126 3212288
>
> 5 ts'Bn<: 120'
> 0.30759069 140800
>
> ([EMAIL PROTECTED] -:Bn@<:) 120
> 1
>
>
> R.E. Boss
>
>
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