Re: [ROOT] strange function

From: Rene Brun (Rene.Brun@cern.ch)
Date: Wed Oct 22 2003 - 08:23:04 MEST


Hi,

You are missing a statement 
  return returnValue;
in your function flux. You have other problems as well in your code.

Rene Brun

Datao Gong wrote:
> 
> Hi,Everyone,
> I just need to caculate some function values. Also it should not be hard
> to draw the funcation. But the Root always complain divided by zero.
> If i do not call the function in the loop, it is fine and get what i
> expect value. Since my code is rathen simple. i paste it here. I use
> Root 3.03 on osf1 system.
> 
> #include "TH1.h"
> #include "TF1.h"
> #include "TROOT.h"
> #include "TStyle.h"
> 
> Double_t f(Double_t z)
> {
> 
>    Double_t returnValue = (1+0.5*z)*(1+0.5*z)*TMath::log(1/z)-
>                           0.5*(1-z)*(3+z);
>    return returnValue;
> 
> }
> 
> Double_t fluxMR(Double_t beam,Double_t m)
> {
>   Double_t s     = 4*beam*beam;
>   Double_t me    = 0.511/1000.0;
>   Double_t alpha = 1/137.036;
> 
>   Double_t  returnValue;
> 
>   Double_t z = m*m/s;
> 
>   Double_t t1 = TMath::log(s/(me*me))-1;
>   Double_t t2 = TMath::log(s/(m*m));
>   returnValue = 3*8*alpha*alpha/(m*m*m)*
>                 ( f(z)*t1*t1-1/3.0*t2*t2*t2 );
> 
> }
> 
> Double_t flux(Double_t *beam, Double_t *par)
> {
> 
>   Double_t etacM      = par[0];
>   Double_t etacPrimeM = par[1];
>   Double_t returnValue = fluxMR(beam[0],etacPrimeM)/fluxMR(beam[0],etacM);
>   return returnValue;
> 
> }
> 
> void calcflux()
> {
>    Double_t par[2];
>    Double_t beam[1];
>    beam[0] = 5.28;
>    par[0] = 2.98;
>    par[1] = 3.64;
> 
>    Double_t res;
>    for(Int_t i = 0 ; i < 100 ; ++i){ //if do not loop, it is fine.
>       beam[0] = 4.7;
> //      beam[0] = 4.7+(5.5-4.7)/100.0*i;
>       cout<<flux(beam,par)<<endl;
> 
>     }
> }
> 
> Thanks
> 
> Gong Datao



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