# Storing multiple TH1::Fit functions with different fit ranges in same histo

From: Remi Mommsen <remigius.mommsen_at_cern.ch>
Date: Thu, 1 Dec 2005 18:36:56 -0600

Dear ROOTers,

I came across a problem trying to fit the same function multiple times to the same hist but using different fit ranges. I like to access the fitted function after each fit for a given range and store their parameters. This works well if I only store the last fitted function, i.e. I do not use the option "+" for TH1::Fit. If I use it, I always get the first stored function back. Is there a solution w/o using a different function in each iteration with an unique name?

The following macro illustrates the problem:

TH1F *trigPt = new TH1F("trigPt", "Pt efficiency", 100, 0, 50);    trigPt->FillRandom("landau");

const Float_t ptbins[5] = {1.5, 3, 5, 10, 50};    Float_t eff[4];
Float_t effSigma[4];
for (Int_t i = 0; i < 4; ++i) {
// case 1: this gets the correct function

trigPt->Fit("pol0","","",ptbins[i],ptbins[i+1]);

// case 2: this does get always the first pol0 function
// trigPt->Fit("pol0","+","",ptbins[i],ptbins[i+1]);

```     eff[i] = trigPt->GetFunction("pol0")->GetParameter(0);
effSigma[i] = trigPt->GetFunction("pol0")->GetParError(0);
std::cout << "Ptbin " << i << ": " << eff[i] << " +/- " <<
```
effSigma[i] << std::endl;

}

Output in case 1:
root [] .x rootbug.C
Fitting results:
Parameters:

```NO.             VALUE           ERROR
0       342.285725      10.681537
```

Ptbin 0: 342.286 +/- 10.6815
Fitting results:
Parameters:
```NO.             VALUE           ERROR
0       172.255836      6.562314
```

Ptbin 1: 172.256 +/- 6.56231
Fitting results:
Parameters:
```NO.             VALUE           ERROR
0       69.657010       2.639261
```

Ptbin 2: 69.657 +/- 2.63926
Fitting results:
Parameters:
```NO.             VALUE           ERROR
0       3.242070        0.205195
```

Ptbin 3: 3.24207 +/- 0.205195

Output in case 2:
note that the cout line always prints the values for function 1 root [] .x rootbug.C
Fitting results:
Parameters:

```NO.             VALUE           ERROR
0       355.334138      10.883231
```

Ptbin 0: 355.334 +/- 10.8832
Fitting results:
Parameters:
```NO.             VALUE           ERROR
0       193.946272      6.963230
```

Ptbin 1: 355.334 +/- 10.8832
Fitting results:
Parameters:
```NO.             VALUE           ERROR
0       67.710358       2.602121
```

Ptbin 2: 355.334 +/- 10.8832
Fitting results:
Parameters:
```NO.             VALUE           ERROR
0       3.305274        0.208544
```

Ptbin 3: 355.334 +/- 10.8832

If it matters: I'm using root 5.06/00 on Mac OS X 10.4.3

Cheers,

Remi

```--
Truth decays into beauty, while beauty soon becomes merely charm.
Charm ends up as strangeness, and even that doesn't last, but up and
down are forever.                                         (Anonymous)

*********************************************************************
Remigius K. Mommsen                 e-mail:          mommsen_at_fnal.gov
University of Manchester               URL:    http://cern.ch/mommsen
Fermilab, MS 357                     voice:        ++1 (630) 840-8321
P.O. Box 500                           fax:        ++1 (630) 840-2649
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```
Received on Fri Dec 02 2005 - 01:38:36 MET

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