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diff --git a/src/Gudhi_stat/include/gudhi/common_persistence_representations.h b/src/Gudhi_stat/include/gudhi/common_persistence_representations.h
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+/*    This file is part of the Gudhi Library. The Gudhi library
+ *    (Geometric Understanding in Higher Dimensions) is a generic C++
+ *    library for computational topology.
+ *
+ *    Author(s):       Pawel Dlotko
+ *
+ *    Copyright (C) 2015  INRIA (France)
+ *
+ *    This program 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.
+ *
+ *    This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef common_gudhi_stat_H
+#define common_gudhi_stat_H
+
+
+namespace Gudhi
+{
+namespace Persistence_representations
+{
+ //this file contain an implementation of some common procedures used in Gudhi_stat.
+
+ //double epsi = std::numeric_limits<double>::epsilon();
+double epsi = 0.000005;
+
+
+
+
+
+/**
+ *  A procedure used to compare doubles. Typically gien two doubles A and B, comparing A == B is not good idea. In this case, we use the procedure almostEqual with the epsi defined at
+ *  the top of the file. Setting up the epsi give the user a tolerance on what should be consider equal.
+**/
+inline bool almost_equal( double a , double b )
+{
+    if ( fabs(a-b) < epsi )
+        return true;
+    return false;
+}
+
+
+
+
+//landscapes
+/**
+ * Extra functions needed in construction of barcodes.
+**/
+double minus_length( std::pair<double,double> a )
+{
+    return a.first-a.second;
+}
+double birth_plus_deaths( std::pair<double,double> a )
+{
+    return a.first+a.second;
+}
+
+
+//landscapes
+/**
+ * Given two points in R^2, the procedure compute the parameters A and B of the line y = Ax + B that crosses those two points.
+**/
+std::pair<double,double> compute_parameters_of_a_line( std::pair<double,double> p1 , std::pair<double,double> p2 )
+{
+    double a = (p2.second-p1.second)/( p2.first - p1.first );
+    double b = p1.second - a*p1.first;
+    return std::make_pair(a,b);
+}
+
+//landscapes
+/**
+ * This procedure given two points which lies on the opposide sides of x axis, compute x for which the line connecting those two points crosses x axis.
+**/
+double find_zero_of_a_line_segment_between_those_two_points ( std::pair<double,double> p1, std::pair<double,double> p2 )
+{
+    if ( p1.first == p2.first )return p1.first;
+    if ( p1.second*p2.second > 0 )
+    {
+        std::ostringstream errMessage;
+        errMessage <<"In function find_zero_of_a_line_segment_between_those_two_points the agguments are: (" << p1.first << "," << p1.second << ") and (" << p2.first << "," << p2.second << "). There is no zero in line between those two points. Program terminated.";
+        std::string errMessageStr = errMessage.str();
+        const char* err = errMessageStr.c_str();
+        throw(err);
+    }
+    //we assume here, that x \in [ p1.first, p2.first ] and p1 and p2 are points between which we will put the line segment
+    double a = (p2.second - p1.second)/(p2.first - p1.first);
+    double b = p1.second - a*p1.first;
+    //cerr << "Line crossing points : (" << p1.first << "," << p1.second << ") oraz (" << p2.first << "," << p2.second << ") : \n";
+    //cerr << "a : " << a << " , b : " << b << " , x : " << x << endl;
+    return -b/a;
+}
+
+
+
+//landscapes
+/**
+ * This method provides a comparision of points that is used in construction of persistence landscapes. The orderign is lexicographical for the first coordinate, and reverse-lexicographical for the 
+ * second coordinate. 
+**/
+bool compare_points_sorting( std::pair<double,double> f, std::pair<double,double> s )
+{
+    if ( f.first < s.first )
+    {
+        return true;
+    }
+    else
+    {//f.first >= s.first
+        if ( f.first > s.first )
+        {
+            return false;
+        }
+        else
+        {//f.first == s.first
+            if ( f.second > s.second )
+            {
+                return true;
+            }
+            else
+            {
+                return false;
+            }
+        }
+    }
+}
+
+
+//landscapes
+/**
+ * This procedure takes two points in R^2 and a double value x. It conputes the line pasing through those two points and return the value of that linear function at x.
+**/
+double function_value ( std::pair<double,double> p1, std::pair<double,double> p2 , double x )
+{
+    //we assume here, that x \in [ p1.first, p2.first ] and p1 and p2 are points between which we will put the line segment
+    double a = (p2.second - p1.second)/(p2.first - p1.first);
+    double b = p1.second - a*p1.first;
+    return (a*x+b);
+}
+
+
+
+
+}//namespace Gudhi_stat
+}//namespace Gudhi
+
+#endif