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"source": [
"# PyROOT Exercise 2: Graphs and Fits"
]
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"source": [
"## Exercise\n",
"\n",
"Write a python macro `ExerciseGraph.py`.\n",
"\n",
"1. Create a graph with symmetric errors and 5 points.\n",
"2. Set the following points:\n",
" `(1.0, 2.1), (2.0, 2.9), (3.0, 4.05), (4.0, 5.2), (5.0, 5.95)`\n",
"3. Set the errors on `x` to 0.0 and the errors on `y` to 0.1 (all at once).\n",
"4. Draw the graph including the axes and error bars.\n",
"5. Create a one dimensional function `f(x) = ax + b` and fit it to the graph.\n",
"\n",
"Bonus questions:\n",
"1. Programatically obtain the two parameters `a` and `b` and their estimated uncertainties."
]
},
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"cell_type": "markdown",
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"source": [
"## Solution"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Welcome to JupyROOT 6.28/00\n"
]
}
],
"source": [
"import ROOT\n",
"%jsroot on"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"a = 1.000000 +/- 0.031623\n",
"b = 1.040000 +/- 0.104881\n",
" FCN=5.7 FROM MIGRAD STATUS=CONVERGED 33 CALLS 34 TOTAL\n",
" EDM=2.71359e-21 STRATEGY= 1 ERROR MATRIX ACCURATE \n",
" EXT PARAMETER STEP FIRST \n",
" NO. NAME VALUE ERROR SIZE DERIVATIVE \n",
" 1 p0 1.00000e+00 3.16228e-02 1.70422e-05 -2.08465e-09\n",
" 2 p1 1.04000e+00 1.04881e-01 5.65226e-05 -1.21781e-09\n"
]
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\n",
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""
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"source": [
"from ROOT import TCanvas, TF1, TGraphErrors\n",
"\n",
"canvas = TCanvas(\"canvas\", \"\", 800, 600)\n",
"\n",
"graph = TGraphErrors(5)\n",
"graph.SetPoint(0, 1.0, 2.1)\n",
"graph.SetPoint(1, 2.0, 2.9)\n",
"graph.SetPoint(2, 3.0, 4.05)\n",
"graph.SetPoint(3, 4.0, 5.2)\n",
"graph.SetPoint(4, 5.0, 5.95)\n",
"for i in range(5):\n",
" graph.SetPointError(i, 0, 0.1)\n",
"\n",
"funct = TF1(\"funct\", \"[0] * x + [1]\", 0, 6)\n",
"graph.Fit(\"funct\")\n",
"\n",
"graph.Draw()\n",
"funct.Draw(\"same\")\n",
"canvas.Draw()\n",
"\n",
"print(f\"a = {funct.GetParameter(0):.6f} +/- {funct.GetParError(0):.6f}\")\n",
"print(f\"b = {funct.GetParameter(1):.6f} +/- {funct.GetParError(1):.6f}\")"
]
}
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