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"# hsimple\n",
" This program creates :\n",
" - a one dimensional histogram\n",
" - a two dimensional histogram\n",
" - a profile histogram\n",
" - a memory-resident ntuple\n",
"\n",
" These objects are filled with some random numbers and saved on a file.\n",
" If get=1 the macro returns a pointer to the TFile of \"hsimple.root\"\n",
" if this file exists, otherwise it is created.\n",
" The file \"hsimple.root\" is created in $ROOTSYS/tutorials if the caller has\n",
" write access to this directory, otherwise the file is created in $PWD\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 08:13 PM."
]
},
{
"cell_type": "markdown",
"id": "8af16151",
"metadata": {},
"source": [
" Arguments are defined. "
]
},
{
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"id": "27ece587",
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"outputs": [],
"source": [
"Int_t getFile=0;"
]
},
{
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"id": "6875fd1b",
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"TString filename = \"hsimple.root\";\n",
"TString dir = gROOT->GetTutorialDir();\n",
"dir.ReplaceAll(\"/./\",\"/\");\n",
"TFile *hfile = nullptr;\n",
"if (getFile) {\n",
" // if the argument getFile =1 return the file \"hsimple.root\"\n",
" // if the file does not exist, it is created\n",
" TString fullPath = dir+\"hsimple.root\";\n",
" if (!gSystem->AccessPathName(fullPath,kFileExists)) {\n",
" hfile = TFile::Open(fullPath); //in $ROOTSYS/tutorials\n",
" if (hfile) return hfile;\n",
" }\n",
" //otherwise try $PWD/hsimple.root\n",
" if (!gSystem->AccessPathName(\"hsimple.root\",kFileExists)) {\n",
" hfile = TFile::Open(\"hsimple.root\"); //in current dir\n",
" if (hfile) return hfile;\n",
" }\n",
"}"
]
},
{
"cell_type": "markdown",
"id": "ff988893",
"metadata": {},
"source": [
"no hsimple.root file found. Must generate it !\n",
"generate hsimple.root in current directory if we have write access"
]
},
{
"cell_type": "code",
"execution_count": 3,
"id": "5af26044",
"metadata": {
"collapsed": false,
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"outputs": [],
"source": [
"if (gSystem->AccessPathName(\".\",kWritePermission)) {\n",
" printf(\"you must run the script in a directory with write access\\n\");\n",
" return nullptr;\n",
"}\n",
"hfile = (TFile*)gROOT->FindObject(filename); if (hfile) hfile->Close();\n",
"hfile = new TFile(filename,\"RECREATE\",\"Demo ROOT file with histograms\");"
]
},
{
"cell_type": "markdown",
"id": "defb12af",
"metadata": {},
"source": [
"Create some histograms, a profile histogram and an ntuple, add them to hfile"
]
},
{
"cell_type": "code",
"execution_count": 4,
"id": "85697db9",
"metadata": {
"collapsed": false,
"execution": {
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"outputs": [],
"source": [
"TH1F *hpx = new TH1F(\"hpx\",\"This is the px distribution\",100,-4,4);\n",
"hpx->SetDirectory(hfile);\n",
"hpx->SetFillColor(48);\n",
"TH2F *hpxpy = new TH2F(\"hpxpy\",\"py vs px\",40,-4,4,40,-4,4);\n",
"hpxpy->SetDirectory(hfile);\n",
"TProfile *hprof = new TProfile(\"hprof\",\"Profile of pz versus px\",100,-4,4,0,20);\n",
"hprof->SetDirectory(hfile);\n",
"TNtuple *ntuple = new TNtuple(\"ntuple\",\"Demo ntuple\",\"px:py:pz:random:i\");"
]
},
{
"cell_type": "markdown",
"id": "836b9e6b",
"metadata": {},
"source": [
"Set to \"true\" if you want to see in the output how much time it took to fill the histogram:"
]
},
{
"cell_type": "code",
"execution_count": 5,
"id": "1b4dea9d",
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"shell.execute_reply": "2026-05-19T20:13:28.799863Z"
}
},
"outputs": [],
"source": [
"const bool doBenchmark = false;\n",
"\n",
"if (doBenchmark)\n",
" gBenchmark->Start(\"hsimple\");"
]
},
{
"cell_type": "markdown",
"id": "90eeb47f",
"metadata": {},
"source": [
"Create a new canvas."
]
},
{
"cell_type": "code",
"execution_count": 6,
"id": "8ecf537e",
"metadata": {
"collapsed": false,
"execution": {
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"source": [
"TCanvas *c1 = new TCanvas(\"c1\",\"Dynamic Filling Example\",200,10,700,500);\n",
"c1->SetFillColor(42);\n",
"c1->GetFrame()->SetFillColor(21);\n",
"c1->GetFrame()->SetBorderSize(6);\n",
"c1->GetFrame()->SetBorderMode(-1);"
]
},
{
"cell_type": "markdown",
"id": "7fa97daa",
"metadata": {},
"source": [
"Fill histograms randomly"
]
},
{
"cell_type": "code",
"execution_count": 7,
"id": "50aa282d",
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"collapsed": false,
"execution": {
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"TRandom3 randomNum;\n",
"Float_t px, py, pz;\n",
"const Int_t kUPDATE = 1000;\n",
"for (Int_t i = 0; i < 25000; i++) {\n",
" randomNum.Rannor(px,py);\n",
" pz = px*px + py*py;\n",
" Float_t rnd = randomNum.Rndm();\n",
" hpx->Fill(px);\n",
" hpxpy->Fill(px,py);\n",
" hprof->Fill(px,pz);\n",
" ntuple->Fill(px,py,pz,rnd,i);\n",
" if (i && (i%kUPDATE) == 0) {\n",
" if (i == kUPDATE) hpx->Draw();\n",
" c1->Modified();\n",
" c1->Update();\n",
" if (gSystem->ProcessEvents())\n",
" break;\n",
" }\n",
"}\n",
"if (doBenchmark)\n",
" gBenchmark->Show(\"hsimple\");"
]
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{
"cell_type": "markdown",
"id": "9feb8e5b",
"metadata": {},
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"Save all objects in this file"
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"hpx->SetFillColor(0);\n",
"hfile->Write();\n",
"hpx->SetFillColor(48);\n",
"c1->Modified();\n",
"return hfile;"
]
},
{
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"id": "647ed4ca",
"metadata": {},
"source": [
"Note that the file is automatically close when application terminates\n",
"or when the file destructor is called."
]
},
{
"cell_type": "markdown",
"id": "c38efef1",
"metadata": {},
"source": [
"Draw all canvases "
]
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