Re: Random Numbers revisited.

From: Rene Brun (Rene.Brun@cern.ch)
Date: Fri Jul 31 1998 - 14:06:13 MEST


Pasha Murat wrote:
> 
> 
> Hello,
>         I feel that I am missing something in the discussion above so I'd
> appreciate to be given a clarification. Let me explain what exactly I'm
> missing:
> 
> - what `hrndm1' does it returns a *single* random number distributed
>   according a probability distribution stored in a given histogram.
> - `FillRandom' methods do very different thing - they *fill a histogram*
>   according to a given probability density stored elsewhere, therefore it seems
>   to me that they miss functionality of `hrndm1' which is quite often needed by
>   the users.
> 
> So is it possible to generate (and retrieve!) a single random number (set of
> numbers) which probability density is stored in a given histogram ?
> 

Currently the following functions are provided
  -TF1::GetRandom returns one number at the time from a theoretical
  function.Note that TF1::GetRandom uses the real integral of
the          function and not just the sum of the function precomputed
for some       bins as it was the case in Hbook for example.

  -TH1::FillRandom(TF1 *) generates a bunch of random numbers
  from a theoretical function (1-d,2-d,3-d) and fill an histogram
  -TH1::FillRandom(TH1 *) generates a bunch of random numbers
  from a histogram (1-d,2-d or 3-d) and fill a histogram.

I could provide a TH1::GetRandom or similar for 2-d and 3-d.
To do that, I must store the integral of the bin contents somewhere
as it is out of question to recompute this integral at every call
like in TH1::FillRandom. I will add this item to my list.


Rene Brun



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