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diff --git a/src/Persistence_representations/include/gudhi/common_persistence_representations.h b/src/Persistence_representations/include/gudhi/common_persistence_representations.h
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+/*    This file is part of the Gudhi Library - https://gudhi.inria.fr/ - which is released under MIT.
+ *    See file LICENSE or go to https://gudhi.inria.fr/licensing/ for full license details.
+ *    Author(s):       Pawel Dlotko
+ *
+ *    Copyright (C) 2016 Inria
+ *
+ *    Modification(s):
+ *      - YYYY/MM Author: Description of the modification
+ */
+
+#ifndef COMMON_PERSISTENCE_REPRESENTATIONS_H_
+#define COMMON_PERSISTENCE_REPRESENTATIONS_H_
+
+#include <utility>
+#include <string>
+#include <cmath>
+#include <boost/math/constants/constants.hpp>
+
+
+
+namespace Gudhi {
+namespace Persistence_representations {
+// this file contain an implementation of some common procedures used in Persistence_representations.
+
+static constexpr double pi = boost::math::constants::pi<double>();
+
+
+/**
+ * In this module, we use the name Persistence_diagram for the representation of a diagram in a vector of pairs of two double.
+ */
+using Persistence_diagram = std::vector<std::pair<double, double> >;
+
+// double epsi = std::numeric_limits<double>::epsilon();
+double epsi = 0.000005;
+
+/**
+ *  A procedure used to compare doubles. Typically given 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 gives the user a tolerance on what should be consider equal.
+**/
+inline bool almost_equal(double a, double b) {
+  if (std::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 opposite 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 arguments 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;
+  return -b / a;
+}
+
+// landscapes
+/**
+ * This method provides a comparison of points that is used in construction of persistence landscapes. The ordering 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 computes the line parsing 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 Persistence_representations
+}  // namespace Gudhi
+
+#endif  // COMMON_PERSISTENCE_REPRESENTATIONS_H_