chi2 problem root

chi2_problem_root

{
 "metadata": {
  "name": "",
  "signature": "sha256:df7234a0e683ce8cb49122683b52f787f9f33e94bdd3a6bc8189dc167e0e2aee"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import numpy as np\n",
      "import matplotlib.pyplot as plt\n",
      "%matplotlib inline"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import ROOT\n",
      "from ROOT import RooFit\n",
      "ROOT.gROOT.GetVersion()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 2,
       "text": [
        "'5.34/24'"
       ]
      }
     ],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "ws = ROOT.RooWorkspace()\n",
      "ws.factory('RooExponential::model(x[0,10], q[-0.05, -1, 1])')\n",
      "\n",
      "x = ws.var('x')\n",
      "model = ws.pdf('model')\n",
      "\n",
      "ws.saveSnapshot(\"initial\", ws.allVars())"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 3,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "chi2s = []\n",
      "chi2s_curve = []\n",
      "\n",
      "for itoy in xrange(500):\n",
      "    ws.loadSnapshot(\"initial\")\n",
      "    data = model.generateBinned(ROOT.RooArgSet(x), 1000)\n",
      "    frame = x.frame()\n",
      "    data.plotOn(frame, RooFit.Name(\"curve_data\"))\n",
      "    model.plotOn(frame, RooFit.Name(\"curve_model\"))\n",
      "    chi2s.append(frame.chiSquare() * x.getBins())\n",
      "    \n",
      "    function = model.asTF(ROOT.RooArgList(x))\n",
      "    curve_data = frame.findObject(\"curve_data\")\n",
      "    chi2s_curve.append(curve_data.Chisquare(function))\n",
      "    \n",
      "print np.mean(chi2s)\n",
      "print np.mean(chi2s_curve)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "76.9831986271\n",
        "878.671902437\n"
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "plt.hist(chi2s);"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "metadata": {},
       "output_type": "display_data",
       "png": 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       "text": [
        "<matplotlib.figure.Figure at 0x2e66b50>"
       ]
      }
     ],
     "prompt_number": 5
    }
   ],
   "metadata": {}
  }
 ]
}