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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