Re: [ROOT] faster TF1::GetRandom()

From: Daniel De Marco (ddm@GE.INFN.IT)
Date: Thu Jan 16 2003 - 12:06:47 MET 

* Daniel De Marco <ddm@ge.infn.it> [15/01/2003 19:26]:
> // return random number
>    Double_t dx = (fXmax-fXmin)/fNpx;
>    Int_t nbinmin=(min-fXmin)/dx;
>    Int_t nbinmax=(max-fXmin)/dx+1;
> 
>     Double_t pmin=fIntegral[nbinmin];
>     Double_t pmax=fIntegral[nbinmax];

I found a wrong behaviour in the code I sent yesterday when max is equal to
the upper limit of the function range.
The above code should be replaced with the code below.

// return random number
   Double_t dx = (fXmax-fXmin)/fNpx;
   Int_t nbinmin=(Int_t)((xmin-fXmin)/dx);
   Int_t nbinmax=(Int_t)((xmax-fXmin)/dx)+2;
   if(nbinmax>fNpx) nbinmax=fNpx;

    Double_t pmin=fIntegral[nbinmin];
    Double_t pmax=fIntegral[nbinmax];

Thanks.
Ciao, Daniel.

--ddm

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