AsymErrors.ipynb

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  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
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   "outputs": [],
   "source": [
    "import ROOT"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
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   },
   "outputs": [
    {
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     "text": [
      "TROOT::Append:0: RuntimeWarning: Replacing existing TH1: h (Potential memory leak).\n"
     ]
    }
   ],
   "source": [
    "h = ROOT.TH1F(\"h\", \"h\", 10, 0, 10)\n",
    "#h.Sumw2()\n",
    "h.Fill(2)\n",
    "h.Fill(2)\n",
    "h.Fill(3)\n",
    "h.Fill(-1)\n",
    "h.SetBinErrorOption(ROOT.TH1F.kPoisson)\n",
    "h.Draw('e')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "from array import array\n",
    "def get_graph_normalized(h):\n",
    "    \"\"\"\n",
    "    Takes as input a TH1F and return a TGraphAsymmErrors\n",
    "    \"\"\"\n",
    "    rh = ROOT.RooHist(h)\n",
    "    norm = h.GetSumOfWeights()\n",
    "    x = array('d', [0])\n",
    "    y = array('d', [0])\n",
    "    for i in xrange(rh.GetN()):\n",
    "        rh.GetPoint(i, x, y)\n",
    "        if y[0] == 0:\n",
    "            rh.SetPointEYhigh(i, 0)\n",
    "            rh.SetPointEYlow(i, 0)\n",
    "        else:\n",
    "            rh.SetPoint(i, x[0], y[0] / norm)\n",
    "            rh.SetPointEYhigh(i, rh.GetErrorYhigh(i) / norm)\n",
    "            rh.SetPointEYlow(i, rh.GetErrorYlow(i) / norm)\n",
    "        \n",
    "    return rh"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "hnorm = get_graph_normalized(h)\n",
    "hnorm.SetFillColor(ROOT.kBlue)\n",
    "hnorm.Draw(\"APE2\")\n",
    "hnorm.Draw(\"P\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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