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Diffstat (limited to 'src/Persistent_cohomology/include/gudhi/Persistent_cohomology/Field_Zp.h')
-rw-r--r-- | src/Persistent_cohomology/include/gudhi/Persistent_cohomology/Field_Zp.h | 104 |
1 files changed, 104 insertions, 0 deletions
diff --git a/src/Persistent_cohomology/include/gudhi/Persistent_cohomology/Field_Zp.h b/src/Persistent_cohomology/include/gudhi/Persistent_cohomology/Field_Zp.h new file mode 100644 index 00000000..0673625c --- /dev/null +++ b/src/Persistent_cohomology/include/gudhi/Persistent_cohomology/Field_Zp.h @@ -0,0 +1,104 @@ +/* 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): Clément Maria + * + * Copyright (C) 2014 Inria + * + * Modification(s): + * - YYYY/MM Author: Description of the modification + */ + +#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_ |