minimization different in ROOT4 and ROOT5

From: Luca Grandi <luca.grandi_at_pv.infn.it>
Date: Thu, 14 Sep 2006 15:11:04 +0200

Hi all,

I have got a problem with minimization using ROOT. I get slightly diffrenet results from ROOT 4 and ROOT 5.

I wrote a script in which I define a histogram  

    hf = new TH1F("hf", "Photoelectrons Spectrum", 200, 0., 1000.);

I fill it

    hf->Fill(data[ev_count]);

and then fit it with a function called "Linear"

TF1 *f1 = new TF1("f1", Linear, 0., 1000., 2);

    f1->SetParameter(0, 1.);
    f1->SetParName(0, "Rho");
    f1->SetParameter(1, 1.);
    f1->SetParName(1, "L.Y. (p.e./keV)");
    c1->cd(1);
    hf->Fit("f1", "L", "", threshold, 1000.);
    hf->Draw("e");

and "Linear" is

Double_t Linear(Double_t *x, Double_t *par) {

    Double_t arg = 0;
    if (par[1] != 0) arg = x[0]/par[1];
    Double_t fitval = par[0]*dNdE(x[0]/par[1])/par[1];     return fitval;
}

If I run it on ROOT 4 I get

FCN=134.135 FROM MIGRAD STATUS=CONVERGED 65 CALLS 66 TOTAL

                      EDM=2.13358e-10    STRATEGY= 1      ERROR
MATRIX ACCURATE
   EXT PARAMETER                                   STEP         FIRST
   NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
    1  Rho          1.78512e+00   6.83244e-02   4.69665e-04   -2.69615e-04

    2 L.Y. (p.e./keV) 1.12079e+00 4.27042e-02 2.93564e-04 6.41165e-05

while if i run ROOT 5 I get

FCN=493.398 FROM MIGRAD    STATUS=CONVERGED      53 CALLS          54 TOTAL
                     EDM=5.30182e-08    STRATEGY= 1      ERROR MATRIX
ACCURATE 
  EXT PARAMETER                                   STEP         FIRST
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
   1  Rho          1.72045e+00   6.75899e-02   4.36268e-04   4.58320e-03

   2 L.Y. (p.e./keV) 1.19107e+00 5.01150e-02 3.24074e-04 1.03245e-02

The results are different as the FCN values. Any suggestion? Received on Thu Sep 14 2006 - 15:11:15 MEST