From 55c7181126aa7defce38c9b82872d14223d4c1dd Mon Sep 17 00:00:00 2001
From: Gard Spreemann <gspreemann@gmail.com>
Date: Tue, 7 Feb 2017 17:33:01 +0100
Subject: Initial import of upstream's 1.3.1.

---
 include/gudhi/Persistent_cohomology/Field_Zp.h | 116 +++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 include/gudhi/Persistent_cohomology/Field_Zp.h

(limited to 'include/gudhi/Persistent_cohomology/Field_Zp.h')

diff --git a/include/gudhi/Persistent_cohomology/Field_Zp.h b/include/gudhi/Persistent_cohomology/Field_Zp.h
new file mode 100644
index 00000000..6db16e69
--- /dev/null
+++ b/include/gudhi/Persistent_cohomology/Field_Zp.h
@@ -0,0 +1,116 @@
+/*    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):       Clément Maria
+ *
+ *    Copyright (C) 2014  INRIA Sophia Antipolis-Méditerranée (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 PERSISTENT_COHOMOLOGY_FIELD_ZP_H_
+#define PERSISTENT_COHOMOLOGY_FIELD_ZP_H_
+
+#include <utility>
+#include <vector>
+
+namespace Gudhi {
+
+namespace persistent_cohomology {
+
+/** \brief Structure representing the coefficient field \f$\mathbb{Z}/p\mathbb{Z}\f$
+ *
+ * \implements CoefficientField
+ * \ingroup persistent_cohomology
+ */
+class Field_Zp {
+ public:
+  typedef int Element;
+
+  Field_Zp()
+      : Prime(0),
+        inverse_() {
+  }
+
+  void init(int charac) {
+    assert(charac > 0);  // division by zero + non negative values
+    Prime = charac;
+    inverse_.clear();
+    inverse_.reserve(charac);
+    inverse_.push_back(0);
+    for (int i = 1; i < Prime; ++i) {
+      int inv = 1;
+      while (((inv * i) % Prime) != 1)
+        ++inv;
+      inverse_.push_back(inv);
+    }
+  }
+
+  /** Set x <- x + w * y*/
+  Element plus_times_equal(const Element& x, const Element& y, const Element& w) {
+    assert(Prime > 0);  // division by zero + non negative values
+    Element result = (x + w * y) % Prime;
+    if (result < 0)
+      result += Prime;
+    return result;
+  }
+
+// operator= defined on Element
+
+  /** Returns y * w */
+  Element times(const Element& y, const Element& w) {
+    return plus_times_equal(0, y, (Element)w);
+  }
+
+  Element plus_equal(const Element& x, const Element& y) {
+    return plus_times_equal(x, y, (Element)1);
+  }
+
+  /** \brief Returns the additive idendity \f$0_{\Bbbk}\f$ of the field.*/
+  Element additive_identity() const {
+    return 0;
+  }
+  /** \brief Returns the multiplicative identity \f$1_{\Bbbk}\f$ of the field.*/
+  Element multiplicative_identity(Element = 0) const {
+    return 1;
+  }
+  /** Returns the inverse in the field. Modifies P. ??? */
+  std::pair<Element, Element> inverse(Element x, Element P) {
+    return std::pair<Element, Element>(inverse_[x], P);
+  }  // <------ return the product of field characteristic for which x is invertible
+
+  /** Returns -x * y.*/
+  Element times_minus(Element x, Element y) {
+    assert(Prime > 0);  // division by zero + non negative values
+    Element out = (-x * y) % Prime;
+    return (out < 0) ? out + Prime : out;
+  }
+
+  /** \brief Returns the characteristic \f$p\f$ of the field.*/
+  int characteristic() const {
+    return Prime;
+  }
+
+ private:
+  int Prime;
+  /** Property map Element -> Element, which associate to an element its inverse in the field.*/
+  std::vector<Element> inverse_;
+};
+
+}  // namespace persistent_cohomology
+
+}  // namespace Gudhi
+
+#endif  // PERSISTENT_COHOMOLOGY_FIELD_ZP_H_
-- 
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