1 files changed, 78 insertions, 0 deletions
diff --git a/src/Coxeter_triangulation/include/gudhi/Functions/Function_whitney_umbrella_in_R3.h b/src/Coxeter_triangulation/include/gudhi/Functions/Function_whitney_umbrella_in_R3.h
new file mode 100644
index 00000000..df1f1eec
--- /dev/null
+++ b/src/Coxeter_triangulation/include/gudhi/Functions/Function_whitney_umbrella_in_R3.h
@@ -0,0 +1,78 @@
+/*    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_WHITNEY_UMBRELLA_IN_R3_H_
+#define FUNCTIONS_FUNCTION_WHITNEY_UMBRELLA_IN_R3_H_
+
+#include <cstdlib>  // for std::size_t
+
+#include <Eigen/Dense>
+
+namespace Gudhi {
+
+namespace coxeter_triangulation {
+
+/**
+ * \class Function_whitney_umbrella_in_R3
+ * \brief A class that encodes the function, the zero-set of which is the Whitney umbrella
+ * surface embedded in R^3.
+ */
+struct Function_whitney_umbrella_in_R3 {
+  /**
+   * \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 {
+    double x = p(0) - off_[0], y = p(1) - off_[1], z = p(2) - off_[2];
+    Eigen::VectorXd result(cod_d());
+    result(0) = x * x - y * y * z;
+    return result;
+  }
+
+  /** \brief Returns the (ambient) domain dimension.*/
+  std::size_t amb_d() const { return 3; };
+
+  /** \brief Returns the codomain dimension. */
+  std::size_t cod_d() const { return 1; };
+
+  /** \brief Returns a point on the surface. This seed point is only one of
+   * two necessary seed points for the manifold tracing algorithm.
+   * See the method seed2() for the other point.
+   */
+  Eigen::VectorXd seed() const {
+    Eigen::Vector3d result(1 + off_[0], 1 + off_[1], 1 + off_[2]);
+    return result;
+  }
+
+  /** \brief Returns a point on the surface. This seed point is only one of
+   * two necessary seed points for the manifold tracing algorithm.
+   * See the method seed() for the other point.
+   */
+  Eigen::VectorXd seed2() const {
+    Eigen::Vector3d result(-1 + off_[0], -1 + off_[1], 1 + off_[2]);
+    return result;
+  }
+
+  /**
+   * \brief Constructor of the function that defines the Whitney umbrella in R^3.
+   *
+   * @param[in] off Offset vector.
+   */
+  Function_whitney_umbrella_in_R3(Eigen::Vector3d off = Eigen::Vector3d::Zero()) : off_(off) {}
+
+ private:
+  Eigen::Vector3d off_;
+};
+
+}  // namespace coxeter_triangulation
+
+}  // namespace Gudhi
+
+#endif