added useful statistical tool script

Scripts/StatisticalTools.C

+//************************************************************************//
+//                                                                        //
+//  Copyright 2018 Bertram Kopf (bertram@ep1.rub.de)                      //
+//                 - Ruhr-Universität Bochum                              //
+//                                                                        //
+//  This file is part of Pawian.                                          //
+//                                                                        //
+//  Pawian is free software: you can redistribute it and/or modify        //
+//  it under the terms of the GNU General Public License as published by  //
+//  the Free Software Foundation, either version 3 of the License, or     //
+//  (at your option) any later version.                                   //
+//                                                                        //
+//  Pawian is distributed in the hope that it will be useful,             //
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of        //
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         //
+//  GNU General Public License for more details.                          //
+//                                                                        //
+//  You should have received a copy of the GNU General Public License     //
+//  along with Pawian.  If not, see <http://www.gnu.org/licenses/>.       //
+//                                                                        //
+//************************************************************************//
+
+#pragma once
+
+//#include "Root.h"
+#include <cmath>
+#include <iostream>
+
+class StatisticalTools
+{
+ public:
+  static double sigmaFromLikelihoodRatio(unsigned double diffLH, unsigned int diffParams){
+    return ROOT::Math::chisquared_quantile_c(TMath::Prob(2.*diffLH, diffParams), 1);
+  }
+
+  static double sigmaFromLikelihoodRatio(double LH1, int ndf1, double LH2, int ndf2){
+    double diffLH=fabs(LH1-LH2);
+    int diffParams=ndf1-ndf2;
+    if(diffParams<0){
+      cout << "ndf2 > ndf1 !!!!\n" 
+           << "this is not supported!!!" << endl;
+      return -10000000000000.;
+    }
+    return sigmaFromLikelihoodRatio(diffLH, diffParams);    
+}
+};