{
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   "source": [
    "# Ifit\n",
    "  Example of a program to fit non-equidistant data points\n",
    "\n",
    "  The fitting function fcn is a simple chisquare function\n",
    "  The data consists of 5 data points (arrays x,y,z) + the errors in errorsz\n",
    "  More details on the various functions or parameters for these functions\n",
    "  can be obtained in an interactive ROOT session with:\n",
    "\n",
    "```cpp\n",
    "   Root > TMinuit *minuit = new TMinuit(10);\n",
    "```\n",
    "\n",
    "```cpp\n",
    "   Root > minuit->mnhelp(\"*\")  to see the list of possible keywords\n",
    "   Root > minuit->mnhelp(\"SET\") explains most parameters\n",
    "```\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "**Author:** Rene Brun  \n",
    "<i><small>This notebook tutorial was automatically generated with <a href= \"https://github.com/root-project/root/blob/master/documentation/doxygen/converttonotebook.py\">ROOTBOOK-izer</a> from the macro found in the ROOT repository  on Tuesday, May 19, 2026 at 08:25 PM.</small></i>"
   ]
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   "source": [
    "%%cpp -d\n",
    "#include \"TMinuit.h\"\n",
    "\n",
    "float z[5],x[5],y[5],errorz[5];"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "8bd67175",
   "metadata": {},
   "source": [
    " ______________________________________________________________________________\n",
    " "
   ]
  },
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   "source": [
    "%%cpp -d\n",
    "double func(float x,float y,double *par)\n",
    "{\n",
    " double value=( (par[0]*par[0])/(x*x)-1)/ ( par[1]+par[2]*y-par[3]*y*y);\n",
    " return value;\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "def06f0c",
   "metadata": {},
   "source": [
    " ______________________________________________________________________________\n",
    " "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "9f5eb273",
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   "source": [
    "%%cpp -d\n",
    "void fcn(int &npar, double *gin, double &f, double *par, int iflag)\n",
    "{\n",
    "   const int nbins = 5;\n",
    "   int i;\n",
    "\n",
    "//calculate chisquare\n",
    "   double chisq = 0;\n",
    "   double delta;\n",
    "   for (i=0;i<nbins; i++) {\n",
    "     delta  = (z[i]-func(x[i],y[i],par))/errorz[i];\n",
    "     chisq += delta*delta;\n",
    "   }\n",
    "   f = chisq;\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "eb4b8824",
   "metadata": {},
   "source": [
    "The z values"
   ]
  },
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   "outputs": [],
   "source": [
    "z[0]=1;\n",
    "z[1]=0.96;\n",
    "z[2]=0.89;\n",
    "z[3]=0.85;\n",
    "z[4]=0.78;"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "709fb54d",
   "metadata": {},
   "source": [
    "The errors on z values"
   ]
  },
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   "cell_type": "code",
   "execution_count": 5,
   "id": "c89f8ae1",
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   "outputs": [],
   "source": [
    "     float error = 0.01;\n",
    "errorz[0]=error;\n",
    "errorz[1]=error;\n",
    "errorz[2]=error;\n",
    "errorz[3]=error;\n",
    "errorz[4]=error;"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "eff0b616",
   "metadata": {},
   "source": [
    "the x values"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "e2a27592",
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   "outputs": [],
   "source": [
    "x[0]=1.5751;\n",
    "x[1]=1.5825;\n",
    "x[2]=1.6069;\n",
    "x[3]=1.6339;\n",
    "x[4]=1.6706;"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "36c3b071",
   "metadata": {},
   "source": [
    "the y values"
   ]
  },
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   "cell_type": "code",
   "execution_count": 7,
   "id": "7dee9d0d",
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    "collapsed": false,
    "execution": {
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " **********\n",
      " **    1 **SET ERR           1\n",
      " **********\n"
     ]
    }
   ],
   "source": [
    "y[0]=1.0642;\n",
    "y[1]=0.97685;\n",
    "y[2]=1.13168;\n",
    "y[3]=1.128654;\n",
    "y[4]=1.44016;\n",
    "\n",
    "TMinuit *gMinuit = new TMinuit(5);  //initialize TMinuit with a maximum of 5 params\n",
    "gMinuit->SetFCN(fcn);\n",
    "\n",
    "double arglist[10];\n",
    "int ierflg = 0;\n",
    "\n",
    "arglist[0] = 1;\n",
    "gMinuit->mnexcm(\"SET ERR\", arglist ,1,ierflg);"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d62475da",
   "metadata": {},
   "source": [
    "Set starting values and step sizes for parameters"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "58c839df",
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   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "input_line_59:4:1: error: reference to 'gMinuit' is ambiguous\n",
      "gMinuit->mnparm(0, \"a1\", vstart[0], step[0], 0,0,ierflg);\n",
      "^\n",
      "input_line_58:8:10: note: candidate found by name lookup is '__cling_N522::gMinuit'\n",
      "TMinuit *gMinuit = new TMinuit(5);  //initialize TMinuit with a maximum of 5 params\n",
      "         ^\n",
      "/github/home/ROOT-CI/build/include/TMinuit.h:271:21: note: candidate found by name lookup is 'gMinuit'\n",
      "R__EXTERN TMinuit  *gMinuit;\n",
      "                    ^\n",
      "input_line_59:5:1: error: reference to 'gMinuit' is ambiguous\n",
      "gMinuit->mnparm(1, \"a2\", vstart[1], step[1], 0,0,ierflg);\n",
      "^\n",
      "input_line_58:8:10: note: candidate found by name lookup is '__cling_N522::gMinuit'\n",
      "TMinuit *gMinuit = new TMinuit(5);  //initialize TMinuit with a maximum of 5 params\n",
      "         ^\n",
      "/github/home/ROOT-CI/build/include/TMinuit.h:271:21: note: candidate found by name lookup is 'gMinuit'\n",
      "R__EXTERN TMinuit  *gMinuit;\n",
      "                    ^\n",
      "input_line_59:6:1: error: reference to 'gMinuit' is ambiguous\n",
      "gMinuit->mnparm(2, \"a3\", vstart[2], step[2], 0,0,ierflg);\n",
      "^\n",
      "input_line_58:8:10: note: candidate found by name lookup is '__cling_N522::gMinuit'\n",
      "TMinuit *gMinuit = new TMinuit(5);  //initialize TMinuit with a maximum of 5 params\n",
      "         ^\n",
      "/github/home/ROOT-CI/build/include/TMinuit.h:271:21: note: candidate found by name lookup is 'gMinuit'\n",
      "R__EXTERN TMinuit  *gMinuit;\n",
      "                    ^\n",
      "input_line_59:7:1: error: reference to 'gMinuit' is ambiguous\n",
      "gMinuit->mnparm(3, \"a4\", vstart[3], step[3], 0,0,ierflg);\n",
      "^\n",
      "input_line_58:8:10: note: candidate found by name lookup is '__cling_N522::gMinuit'\n",
      "TMinuit *gMinuit = new TMinuit(5);  //initialize TMinuit with a maximum of 5 params\n",
      "         ^\n",
      "/github/home/ROOT-CI/build/include/TMinuit.h:271:21: note: candidate found by name lookup is 'gMinuit'\n",
      "R__EXTERN TMinuit  *gMinuit;\n",
      "                    ^\n"
     ]
    }
   ],
   "source": [
    "static double vstart[4] = {3, 1 , 0.1 , 0.01};\n",
    "static double step[4] = {0.1 , 0.1 , 0.01 , 0.001};\n",
    "gMinuit->mnparm(0, \"a1\", vstart[0], step[0], 0,0,ierflg);\n",
    "gMinuit->mnparm(1, \"a2\", vstart[1], step[1], 0,0,ierflg);\n",
    "gMinuit->mnparm(2, \"a3\", vstart[2], step[2], 0,0,ierflg);\n",
    "gMinuit->mnparm(3, \"a4\", vstart[3], step[3], 0,0,ierflg);"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "7920f21e",
   "metadata": {},
   "source": [
    "Now ready for minimization step"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "ac7c7979",
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    }
   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "input_line_60:4:1: error: reference to 'gMinuit' is ambiguous\n",
      "gMinuit->mnexcm(\"MIGRAD\", arglist ,2,ierflg);\n",
      "^\n",
      "input_line_58:8:10: note: candidate found by name lookup is '__cling_N522::gMinuit'\n",
      "TMinuit *gMinuit = new TMinuit(5);  //initialize TMinuit with a maximum of 5 params\n",
      "         ^\n",
      "/github/home/ROOT-CI/build/include/TMinuit.h:271:21: note: candidate found by name lookup is 'gMinuit'\n",
      "R__EXTERN TMinuit  *gMinuit;\n",
      "                    ^\n"
     ]
    }
   ],
   "source": [
    "arglist[0] = 500;\n",
    "arglist[1] = 1.;\n",
    "gMinuit->mnexcm(\"MIGRAD\", arglist ,2,ierflg);"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "83e131db",
   "metadata": {},
   "source": [
    "Print results"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "cda17669",
   "metadata": {
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    }
   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "input_line_61:4:1: error: reference to 'gMinuit' is ambiguous\n",
      "gMinuit->mnstat(amin,edm,errdef,nvpar,nparx,icstat);\n",
      "^\n",
      "input_line_58:8:10: note: candidate found by name lookup is '__cling_N522::gMinuit'\n",
      "TMinuit *gMinuit = new TMinuit(5);  //initialize TMinuit with a maximum of 5 params\n",
      "         ^\n",
      "/github/home/ROOT-CI/build/include/TMinuit.h:271:21: note: candidate found by name lookup is 'gMinuit'\n",
      "R__EXTERN TMinuit  *gMinuit;\n",
      "                    ^\n"
     ]
    }
   ],
   "source": [
    "double amin,edm,errdef;\n",
    "int nvpar,nparx,icstat;\n",
    "gMinuit->mnstat(amin,edm,errdef,nvpar,nparx,icstat);"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9a6300df",
   "metadata": {},
   "source": [
    "gMinuit->mnprin(3,amin);"
   ]
  }
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