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"# fit1\n",
"Simple fitting example (1-d histogram with an interpreted function)\n",
"\n",
"\n",
"\n",
"\n",
"**Author:** Rene Brun \n",
"This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, May 19, 2026 at 08:24 PM."
]
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"TCanvas *c1 = new TCanvas(\"c1_fit1\",\"The Fit Canvas\",200,10,700,500);\n",
"c1->SetGridx();\n",
"c1->SetGridy();\n",
"c1->GetFrame()->SetFillColor(21);\n",
"c1->GetFrame()->SetBorderMode(-1);\n",
"c1->GetFrame()->SetBorderSize(5);"
]
},
{
"cell_type": "markdown",
"id": "c8ffc1a9",
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"source": [
"(for more details, see\n",
"filling histograms with random numbers from a function)"
]
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"TFormula *form1 = new TFormula(\"form1\", \"abs(sin(x)/x)\");\n",
"TF1 *sqroot = new TF1(\"sqroot\", \"x*gaus(0) + [3]*form1\", 0.0, 10.0);\n",
"sqroot->SetLineColor(4);\n",
"sqroot->SetLineWidth(6);"
]
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{
"cell_type": "markdown",
"id": "776814f1",
"metadata": {},
"source": [
"Set parameters to the functions \"gaus\" and \"form1\"."
]
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"Formula based function: sqroot \n",
" sqroot : x*gaus(0) + [3]*form1 Ndim= 1, Npar= 4, Number= 0 \n",
" Formula expression: \n",
"\tx*[p0]*exp(-0.5*((x-[p1])/[p2])*((x-[p1])/[p2]))+[p3]*(abs(sin(x)/x)) \n"
]
}
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"source": [
"sqroot->SetParameters(10.0, 4.0, 1.0, 20.0);\n",
"sqroot->Print();\n",
"\n",
"TH1D *h1d = new TH1D(\"h1d\", \"Test random numbers\", 200, 0.0, 10.0);\n",
"h1d->FillRandom(\"sqroot\", 10000);"
]
},
{
"cell_type": "markdown",
"id": "befb66f6",
"metadata": {},
"source": [
"Now fit histogram h1d with the function sqroot"
]
},
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"text": [
"****************************************\n",
"Minimizer is Minuit2 / Migrad\n",
"Chi2 = 198.935\n",
"NDf = 190\n",
"Edm = 1.49283e-07\n",
"NCalls = 149\n",
"p0 = 33.1658 +/- 0.545703 \n",
"p1 = 4.00667 +/- 0.0165304 \n",
"p2 = 0.984663 +/- 0.0128238 \n",
"p3 = 63.4464 +/- 1.33233 \n"
]
}
],
"source": [
"h1d->SetFillColor(45);\n",
"h1d->Fit(\"sqroot\");"
]
},
{
"cell_type": "markdown",
"id": "8bfbf428",
"metadata": {},
"source": [
"We now annotate the picture by creating a PaveText object\n",
"and displaying the list of commands in this macro"
]
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"TString dir = gROOT->GetTutorialDir();\n",
"dir.Append(\"/math/fit/\");\n",
"TPaveText * fitlabel = new TPaveText(0.6,0.4,0.9,0.75,\"NDC\");\n",
"fitlabel->SetTextAlign(12);\n",
"fitlabel->SetFillColor(42);\n",
"fitlabel->ReadFile(Form(\"%sfit1_C.txt\", dir.Data()));\n",
"fitlabel->Draw();\n",
"c1->Update();"
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"source": [
"Draw all canvases "
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