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diff --git a/src/Coxeter_triangulation/include/gudhi/Functions/Function_Sm_in_Rd.h b/src/Coxeter_triangulation/include/gudhi/Functions/Function_Sm_in_Rd.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):       Siargey Kachanovich
+ *
+ *    Copyright (C) 2019 Inria
+ *
+ *    Modification(s):
+ *      - YYYY/MM Author: Description of the modification
+ */
+
+#ifndef FUNCTIONS_FUNCTION_SM_IN_RD_H_
+#define FUNCTIONS_FUNCTION_SM_IN_RD_H_
+
+#include <cstdlib>  // for std::size_t
+
+#include <Eigen/Dense>
+
+namespace Gudhi {
+
+namespace coxeter_triangulation {
+
+/**
+ * \class Function_Sm_in_Rd
+ * \brief A class for the function that defines an m-dimensional implicit sphere embedded
+ * in the d-dimensional Euclidean space.
+ */
+struct Function_Sm_in_Rd {
+  /** \brief Value of the function at a specified point.
+   * @param[in] p The input point. The dimension needs to coincide with the ambient dimension.
+   */
+  Eigen::VectorXd operator()(const Eigen::VectorXd& p) const {
+    Eigen::VectorXd x = p;
+    for (std::size_t i = 0; i < d_; ++i) x(i) -= center_[i];
+    Eigen::VectorXd result = Eigen::VectorXd::Zero(k_);
+    for (std::size_t i = 0; i < m_ + 1; ++i) result(0) += x(i) * x(i);
+    result(0) -= r_ * r_;
+    for (std::size_t j = 1; j < k_; ++j) result(j) = x(m_ + j);
+    return result;
+  }
+
+  /** \brief Returns the domain dimension. Same as the ambient dimension of the sphere. */
+  std::size_t amb_d() const { return d_; };
+
+  /** \brief Returns the codomain dimension. Same as the codimension of the sphere. */
+  std::size_t cod_d() const { return k_; };
+
+  /** \brief Returns a point on the sphere. */
+  Eigen::VectorXd seed() const {
+    Eigen::VectorXd result = Eigen::VectorXd::Zero(d_);
+    result(0) += r_;
+    for (std::size_t i = 0; i < d_; ++i) result(i) += center_[i];
+    return result;
+  }
+
+  /**
+   * \brief Constructor of the function that defines an m-dimensional implicit sphere embedded
+   * in the d-dimensional Euclidean space.
+   *
+   * @param[in] r The radius of the sphere.
+   * @param[in] m The dimension of the sphere.
+   * @param[in] d The ambient dimension of the sphere.
+   * @param[in] center The center of the sphere.
+   */
+  Function_Sm_in_Rd(double r, std::size_t m, std::size_t d, Eigen::VectorXd center)
+      : m_(m), k_(d - m), d_(d), r_(r), center_(center) {}
+
+  /**
+   * \brief Constructor of the function that defines an m-dimensional implicit sphere embedded
+   * in the d-dimensional Euclidean space centered at the origin.
+   *
+   * @param[in] r The radius of the sphere.
+   * @param[in] m The dimension of the sphere.
+   * @param[in] d The ambient dimension of the sphere.
+   */
+  Function_Sm_in_Rd(double r, std::size_t m, std::size_t d)
+      : m_(m), k_(d - m), d_(d), r_(r), center_(Eigen::VectorXd::Zero(d_)) {}
+
+  /**
+   * \brief Constructor of the function that defines an m-dimensional implicit sphere embedded
+   * in the (m+1)-dimensional Euclidean space.
+   *
+   * @param[in] r The radius of the sphere.
+   * @param[in] m The dimension of the sphere.
+   * @param[in] center The center of the sphere.
+   */
+  Function_Sm_in_Rd(double r, std::size_t m, Eigen::VectorXd center)
+      : m_(m), k_(1), d_(m_ + 1), r_(r), center_(center) {}
+
+  /**
+   * \brief Constructor of the function that defines an m-dimensional implicit sphere embedded
+   * in the (m+1)-dimensional Euclidean space centered at the origin.
+   *
+   * @param[in] r The radius of the sphere.
+   * @param[in] m The dimension of the sphere.
+   */
+  Function_Sm_in_Rd(double r, std::size_t m) : m_(m), k_(1), d_(m_ + 1), r_(r), center_(Eigen::VectorXd::Zero(d_)) {}
+
+  Function_Sm_in_Rd(const Function_Sm_in_Rd& rhs) : Function_Sm_in_Rd(rhs.r_, rhs.m_, rhs.d_, rhs.center_) {}
+
+ private:
+  std::size_t m_, k_, d_;
+  double r_;
+  Eigen::VectorXd center_;
+};
+
+}  // namespace coxeter_triangulation
+
+}  // namespace Gudhi
+
+#endif