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"# hist019_TH2_projection\n",
"A TExec allows to redraw automatically the projections when a zoom is performed\n",
"on the 2D histogram.\n",
"\n",
"\n",
"\n",
"\n",
"**Author:** Olivier Couet \n",
"This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, May 19, 2026 at 08:12 PM."
]
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"source": [
"TH2F *h2;\n",
"TH1D *projh2X;\n",
"TH1D *projh2Y;\n",
"TPad *right_pad, *top_pad;"
]
},
{
"cell_type": "markdown",
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" Definition of a helper function: "
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"source": [
"%%cpp -d\n",
"void ZoomExec()\n",
"{\n",
" int xfirst = h2->GetXaxis()->GetFirst();\n",
" int xlast = h2->GetXaxis()->GetLast();\n",
" double xmin = h2->GetXaxis()->GetBinLowEdge(xfirst);\n",
" double xmax = h2->GetXaxis()->GetBinUpEdge(xlast);\n",
" projh2X->GetXaxis()->SetRangeUser(xmin, xmax);\n",
" top_pad->Modified();\n",
"\n",
" int yfirst = h2->GetYaxis()->GetFirst();\n",
" int ylast = h2->GetYaxis()->GetLast();\n",
" double ymin = h2->GetYaxis()->GetBinLowEdge(yfirst);\n",
" double ymax = h2->GetYaxis()->GetBinUpEdge(ylast);\n",
" projh2Y->GetXaxis()->SetRangeUser(ymin, ymax);\n",
" right_pad->Modified();\n",
"}"
]
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"source": [
"auto c1 = new TCanvas(\"c1\", \"c1\", 900, 900);\n",
"gStyle->SetOptStat(0);\n",
"\n",
"TPad *center_pad = new TPad(\"center_pad\", \"center_pad\", 0.0, 0.0, 0.6, 0.6);\n",
"center_pad->Draw();\n",
"\n",
"right_pad = new TPad(\"right_pad\", \"right_pad\", 0.55, 0.0, 1.0, 0.6);\n",
"right_pad->Draw();\n",
"\n",
"top_pad = new TPad(\"top_pad\", \"top_pad\", 0.0, 0.55, 0.6, 1.0);\n",
"top_pad->Draw();\n",
"\n",
"h2 = new TH2F(\"h2\", \"\", 40, -4, 4, 40, -20, 20);\n",
"Float_t px, py;\n",
"for (Int_t i = 0; i < 25000; i++) {\n",
" gRandom->Rannor(px, py);\n",
" h2->Fill(px, 5 * py);\n",
"}\n",
"projh2X = h2->ProjectionX();\n",
"projh2Y = h2->ProjectionY();\n",
"\n",
"center_pad->cd();\n",
"gStyle->SetPalette(1);\n",
"h2->Draw(\"COL\");\n",
"\n",
"top_pad->cd();\n",
"projh2X->SetFillColor(kBlue + 1);\n",
"projh2X->Draw(\"bar\");\n",
"\n",
"right_pad->cd();\n",
"projh2Y->SetFillColor(kBlue - 2);\n",
"projh2Y->Draw(\"hbar\");\n",
"\n",
"c1->cd();\n",
"TLatex t;\n",
"t.SetTextFont(42);\n",
"t.SetTextSize(0.02);\n",
"t.DrawLatex(0.6, 0.88, \"This example demonstrates how to display\");\n",
"t.DrawLatex(0.6, 0.85, \"a histogram and its two projections.\");\n",
"\n",
"auto ex = new TExec(\"zoom\", \"ZoomExec()\");\n",
"h2->GetListOfFunctions()->Add(ex);"
]
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"metadata": {},
"source": [
"Draw all canvases "
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],
"source": [
"%jsroot on\n",
"gROOT->GetListOfCanvases()->Draw()"
]
}
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