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include/Eigen/src/Core/PermutationMatrix.h

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+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2009 Benoit Jacob <jacob.benoit.1@gmail.com>
+// Copyright (C) 2009-2015 Gael Guennebaud <gael.guennebaud@inria.fr>
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef EIGEN_PERMUTATIONMATRIX_H
+#define EIGEN_PERMUTATIONMATRIX_H
+
+// IWYU pragma: private
+#include "./InternalHeaderCheck.h"
+
+namespace Eigen {
+
+namespace internal {
+
+enum PermPermProduct_t { PermPermProduct };
+
+}  // end namespace internal
+
+/** \class PermutationBase
+ * \ingroup Core_Module
+ *
+ * \brief Base class for permutations
+ *
+ * \tparam Derived the derived class
+ *
+ * This class is the base class for all expressions representing a permutation matrix,
+ * internally stored as a vector of integers.
+ * The convention followed here is that if \f$ \sigma \f$ is a permutation, the corresponding permutation matrix
+ * \f$ P_\sigma \f$ is such that if \f$ (e_1,\ldots,e_p) \f$ is the canonical basis, we have:
+ *  \f[ P_\sigma(e_i) = e_{\sigma(i)}. \f]
+ * This convention ensures that for any two permutations \f$ \sigma, \tau \f$, we have:
+ *  \f[ P_{\sigma\circ\tau} = P_\sigma P_\tau. \f]
+ *
+ * Permutation matrices are square and invertible.
+ *
+ * Notice that in addition to the member functions and operators listed here, there also are non-member
+ * operator* to multiply any kind of permutation object with any kind of matrix expression (MatrixBase)
+ * on either side.
+ *
+ * \sa class PermutationMatrix, class PermutationWrapper
+ */
+template <typename Derived>
+class PermutationBase : public EigenBase<Derived> {
+  typedef internal::traits<Derived> Traits;
+  typedef EigenBase<Derived> Base;
+
+ public:
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  typedef typename Traits::IndicesType IndicesType;
+  enum {
+    Flags = Traits::Flags,
+    RowsAtCompileTime = Traits::RowsAtCompileTime,
+    ColsAtCompileTime = Traits::ColsAtCompileTime,
+    MaxRowsAtCompileTime = Traits::MaxRowsAtCompileTime,
+    MaxColsAtCompileTime = Traits::MaxColsAtCompileTime
+  };
+  typedef typename Traits::StorageIndex StorageIndex;
+  typedef Matrix<StorageIndex, RowsAtCompileTime, ColsAtCompileTime, 0, MaxRowsAtCompileTime, MaxColsAtCompileTime>
+      DenseMatrixType;
+  typedef PermutationMatrix<IndicesType::SizeAtCompileTime, IndicesType::MaxSizeAtCompileTime, StorageIndex>
+      PlainPermutationType;
+  typedef PlainPermutationType PlainObject;
+  using Base::derived;
+  typedef Inverse<Derived> InverseReturnType;
+  typedef void Scalar;
+#endif
+
+  /** Copies the other permutation into *this */
+  template <typename OtherDerived>
+  Derived& operator=(const PermutationBase<OtherDerived>& other) {
+    indices() = other.indices();
+    return derived();
+  }
+
+  /** Assignment from the Transpositions \a tr */
+  template <typename OtherDerived>
+  Derived& operator=(const TranspositionsBase<OtherDerived>& tr) {
+    setIdentity(tr.size());
+    for (Index k = size() - 1; k >= 0; --k) applyTranspositionOnTheRight(k, tr.coeff(k));
+    return derived();
+  }
+
+  /** \returns the number of rows */
+  inline EIGEN_DEVICE_FUNC Index rows() const { return Index(indices().size()); }
+
+  /** \returns the number of columns */
+  inline EIGEN_DEVICE_FUNC Index cols() const { return Index(indices().size()); }
+
+  /** \returns the size of a side of the respective square matrix, i.e., the number of indices */
+  inline EIGEN_DEVICE_FUNC Index size() const { return Index(indices().size()); }
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  template <typename DenseDerived>
+  void evalTo(MatrixBase<DenseDerived>& other) const {
+    other.setZero();
+    for (Index i = 0; i < rows(); ++i) other.coeffRef(indices().coeff(i), i) = typename DenseDerived::Scalar(1);
+  }
+#endif
+
+  /** \returns a Matrix object initialized from this permutation matrix. Notice that it
+   * is inefficient to return this Matrix object by value. For efficiency, favor using
+   * the Matrix constructor taking EigenBase objects.
+   */
+  DenseMatrixType toDenseMatrix() const { return derived(); }
+
+  /** const version of indices(). */
+  const IndicesType& indices() const { return derived().indices(); }
+  /** \returns a reference to the stored array representing the permutation. */
+  IndicesType& indices() { return derived().indices(); }
+
+  /** Resizes to given size.
+   */
+  inline void resize(Index newSize) { indices().resize(newSize); }
+
+  /** Sets *this to be the identity permutation matrix */
+  void setIdentity() {
+    StorageIndex n = StorageIndex(size());
+    for (StorageIndex i = 0; i < n; ++i) indices().coeffRef(i) = i;
+  }
+
+  /** Sets *this to be the identity permutation matrix of given size.
+   */
+  void setIdentity(Index newSize) {
+    resize(newSize);
+    setIdentity();
+  }
+
+  /** Multiplies *this by the transposition \f$(ij)\f$ on the left.
+   *
+   * \returns a reference to *this.
+   *
+   * \warning This is much slower than applyTranspositionOnTheRight(Index,Index):
+   * this has linear complexity and requires a lot of branching.
+   *
+   * \sa applyTranspositionOnTheRight(Index,Index)
+   */
+  Derived& applyTranspositionOnTheLeft(Index i, Index j) {
+    eigen_assert(i >= 0 && j >= 0 && i < size() && j < size());
+    for (Index k = 0; k < size(); ++k) {
+      if (indices().coeff(k) == i)
+        indices().coeffRef(k) = StorageIndex(j);
+      else if (indices().coeff(k) == j)
+        indices().coeffRef(k) = StorageIndex(i);
+    }
+    return derived();
+  }
+
+  /** Multiplies *this by the transposition \f$(ij)\f$ on the right.
+   *
+   * \returns a reference to *this.
+   *
+   * This is a fast operation, it only consists in swapping two indices.
+   *
+   * \sa applyTranspositionOnTheLeft(Index,Index)
+   */
+  Derived& applyTranspositionOnTheRight(Index i, Index j) {
+    eigen_assert(i >= 0 && j >= 0 && i < size() && j < size());
+    std::swap(indices().coeffRef(i), indices().coeffRef(j));
+    return derived();
+  }
+
+  /** \returns the inverse permutation matrix.
+   *
+   * \note \blank \note_try_to_help_rvo
+   */
+  inline InverseReturnType inverse() const { return InverseReturnType(derived()); }
+  /** \returns the transpose permutation matrix.
+   *
+   * \note \blank \note_try_to_help_rvo
+   */
+  inline InverseReturnType transpose() const { return InverseReturnType(derived()); }
+
+  /**** multiplication helpers to hopefully get RVO ****/
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+ protected:
+  template <typename OtherDerived>
+  void assignTranspose(const PermutationBase<OtherDerived>& other) {
+    for (Index i = 0; i < rows(); ++i) indices().coeffRef(other.indices().coeff(i)) = i;
+  }
+  template <typename Lhs, typename Rhs>
+  void assignProduct(const Lhs& lhs, const Rhs& rhs) {
+    eigen_assert(lhs.cols() == rhs.rows());
+    for (Index i = 0; i < rows(); ++i) indices().coeffRef(i) = lhs.indices().coeff(rhs.indices().coeff(i));
+  }
+#endif
+
+ public:
+  /** \returns the product permutation matrix.
+   *
+   * \note \blank \note_try_to_help_rvo
+   */
+  template <typename Other>
+  inline PlainPermutationType operator*(const PermutationBase<Other>& other) const {
+    return PlainPermutationType(internal::PermPermProduct, derived(), other.derived());
+  }
+
+  /** \returns the product of a permutation with another inverse permutation.
+   *
+   * \note \blank \note_try_to_help_rvo
+   */
+  template <typename Other>
+  inline PlainPermutationType operator*(const InverseImpl<Other, PermutationStorage>& other) const {
+    return PlainPermutationType(internal::PermPermProduct, *this, other.eval());
+  }
+
+  /** \returns the product of an inverse permutation with another permutation.
+   *
+   * \note \blank \note_try_to_help_rvo
+   */
+  template <typename Other>
+  friend inline PlainPermutationType operator*(const InverseImpl<Other, PermutationStorage>& other,
+                                               const PermutationBase& perm) {
+    return PlainPermutationType(internal::PermPermProduct, other.eval(), perm);
+  }
+
+  /** \returns the determinant of the permutation matrix, which is either 1 or -1 depending on the parity of the
+   * permutation.
+   *
+   * This function is O(\c n) procedure allocating a buffer of \c n booleans.
+   */
+  Index determinant() const {
+    Index res = 1;
+    Index n = size();
+    Matrix<bool, RowsAtCompileTime, 1, 0, MaxRowsAtCompileTime> mask(n);
+    mask.fill(false);
+    Index r = 0;
+    while (r < n) {
+      // search for the next seed
+      while (r < n && mask[r]) r++;
+      if (r >= n) break;
+      // we got one, let's follow it until we are back to the seed
+      Index k0 = r++;
+      mask.coeffRef(k0) = true;
+      for (Index k = indices().coeff(k0); k != k0; k = indices().coeff(k)) {
+        mask.coeffRef(k) = true;
+        res = -res;
+      }
+    }
+    return res;
+  }
+
+ protected:
+};
+
+namespace internal {
+template <int SizeAtCompileTime, int MaxSizeAtCompileTime, typename StorageIndex_>
+struct traits<PermutationMatrix<SizeAtCompileTime, MaxSizeAtCompileTime, StorageIndex_> >
+    : traits<
+          Matrix<StorageIndex_, SizeAtCompileTime, SizeAtCompileTime, 0, MaxSizeAtCompileTime, MaxSizeAtCompileTime> > {
+  typedef PermutationStorage StorageKind;
+  typedef Matrix<StorageIndex_, SizeAtCompileTime, 1, 0, MaxSizeAtCompileTime, 1> IndicesType;
+  typedef StorageIndex_ StorageIndex;
+  typedef void Scalar;
+};
+}  // namespace internal
+
+/** \class PermutationMatrix
+ * \ingroup Core_Module
+ *
+ * \brief Permutation matrix
+ *
+ * \tparam SizeAtCompileTime the number of rows/cols, or Dynamic
+ * \tparam MaxSizeAtCompileTime the maximum number of rows/cols, or Dynamic. This optional parameter defaults to
+ * SizeAtCompileTime. Most of the time, you should not have to specify it. \tparam StorageIndex_ the integer type of the
+ * indices
+ *
+ * This class represents a permutation matrix, internally stored as a vector of integers.
+ *
+ * \sa class PermutationBase, class PermutationWrapper, class DiagonalMatrix
+ */
+template <int SizeAtCompileTime, int MaxSizeAtCompileTime, typename StorageIndex_>
+class PermutationMatrix
+    : public PermutationBase<PermutationMatrix<SizeAtCompileTime, MaxSizeAtCompileTime, StorageIndex_> > {
+  typedef PermutationBase<PermutationMatrix> Base;
+  typedef internal::traits<PermutationMatrix> Traits;
+
+ public:
+  typedef const PermutationMatrix& Nested;
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  typedef typename Traits::IndicesType IndicesType;
+  typedef typename Traits::StorageIndex StorageIndex;
+#endif
+
+  inline PermutationMatrix() {}
+
+  /** Constructs an uninitialized permutation matrix of given size.
+   */
+  explicit inline PermutationMatrix(Index size) : m_indices(size) {
+    eigen_internal_assert(size <= NumTraits<StorageIndex>::highest());
+  }
+
+  /** Copy constructor. */
+  template <typename OtherDerived>
+  inline PermutationMatrix(const PermutationBase<OtherDerived>& other) : m_indices(other.indices()) {}
+
+  /** Generic constructor from expression of the indices. The indices
+   * array has the meaning that the permutations sends each integer i to indices[i].
+   *
+   * \warning It is your responsibility to check that the indices array that you passes actually
+   * describes a permutation, i.e., each value between 0 and n-1 occurs exactly once, where n is the
+   * array's size.
+   */
+  template <typename Other>
+  explicit inline PermutationMatrix(const MatrixBase<Other>& indices) : m_indices(indices) {}
+
+  /** Convert the Transpositions \a tr to a permutation matrix */
+  template <typename Other>
+  explicit PermutationMatrix(const TranspositionsBase<Other>& tr) : m_indices(tr.size()) {
+    *this = tr;
+  }
+
+  /** Copies the other permutation into *this */
+  template <typename Other>
+  PermutationMatrix& operator=(const PermutationBase<Other>& other) {
+    m_indices = other.indices();
+    return *this;
+  }
+
+  /** Assignment from the Transpositions \a tr */
+  template <typename Other>
+  PermutationMatrix& operator=(const TranspositionsBase<Other>& tr) {
+    return Base::operator=(tr.derived());
+  }
+
+  /** const version of indices(). */
+  const IndicesType& indices() const { return m_indices; }
+  /** \returns a reference to the stored array representing the permutation. */
+  IndicesType& indices() { return m_indices; }
+
+  /**** multiplication helpers to hopefully get RVO ****/
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  template <typename Other>
+  PermutationMatrix(const InverseImpl<Other, PermutationStorage>& other)
+      : m_indices(other.derived().nestedExpression().size()) {
+    eigen_internal_assert(m_indices.size() <= NumTraits<StorageIndex>::highest());
+    StorageIndex end = StorageIndex(m_indices.size());
+    for (StorageIndex i = 0; i < end; ++i)
+      m_indices.coeffRef(other.derived().nestedExpression().indices().coeff(i)) = i;
+  }
+  template <typename Lhs, typename Rhs>
+  PermutationMatrix(internal::PermPermProduct_t, const Lhs& lhs, const Rhs& rhs) : m_indices(lhs.indices().size()) {
+    Base::assignProduct(lhs, rhs);
+  }
+#endif
+
+ protected:
+  IndicesType m_indices;
+};
+
+namespace internal {
+template <int SizeAtCompileTime, int MaxSizeAtCompileTime, typename StorageIndex_, int PacketAccess_>
+struct traits<Map<PermutationMatrix<SizeAtCompileTime, MaxSizeAtCompileTime, StorageIndex_>, PacketAccess_> >
+    : traits<
+          Matrix<StorageIndex_, SizeAtCompileTime, SizeAtCompileTime, 0, MaxSizeAtCompileTime, MaxSizeAtCompileTime> > {
+  typedef PermutationStorage StorageKind;
+  typedef Map<const Matrix<StorageIndex_, SizeAtCompileTime, 1, 0, MaxSizeAtCompileTime, 1>, PacketAccess_> IndicesType;
+  typedef StorageIndex_ StorageIndex;
+  typedef void Scalar;
+};
+}  // namespace internal
+
+template <int SizeAtCompileTime, int MaxSizeAtCompileTime, typename StorageIndex_, int PacketAccess_>
+class Map<PermutationMatrix<SizeAtCompileTime, MaxSizeAtCompileTime, StorageIndex_>, PacketAccess_>
+    : public PermutationBase<
+          Map<PermutationMatrix<SizeAtCompileTime, MaxSizeAtCompileTime, StorageIndex_>, PacketAccess_> > {
+  typedef PermutationBase<Map> Base;
+  typedef internal::traits<Map> Traits;
+
+ public:
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  typedef typename Traits::IndicesType IndicesType;
+  typedef typename IndicesType::Scalar StorageIndex;
+#endif
+
+  inline Map(const StorageIndex* indicesPtr) : m_indices(indicesPtr) {}
+
+  inline Map(const StorageIndex* indicesPtr, Index size) : m_indices(indicesPtr, size) {}
+
+  /** Copies the other permutation into *this */
+  template <typename Other>
+  Map& operator=(const PermutationBase<Other>& other) {
+    return Base::operator=(other.derived());
+  }
+
+  /** Assignment from the Transpositions \a tr */
+  template <typename Other>
+  Map& operator=(const TranspositionsBase<Other>& tr) {
+    return Base::operator=(tr.derived());
+  }
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  /** This is a special case of the templated operator=. Its purpose is to
+   * prevent a default operator= from hiding the templated operator=.
+   */
+  Map& operator=(const Map& other) {
+    m_indices = other.m_indices;
+    return *this;
+  }
+#endif
+
+  /** const version of indices(). */
+  const IndicesType& indices() const { return m_indices; }
+  /** \returns a reference to the stored array representing the permutation. */
+  IndicesType& indices() { return m_indices; }
+
+ protected:
+  IndicesType m_indices;
+};
+
+template <typename IndicesType_>
+class TranspositionsWrapper;
+namespace internal {
+template <typename IndicesType_>
+struct traits<PermutationWrapper<IndicesType_> > {
+  typedef PermutationStorage StorageKind;
+  typedef void Scalar;
+  typedef typename IndicesType_::Scalar StorageIndex;
+  typedef IndicesType_ IndicesType;
+  enum {
+    RowsAtCompileTime = IndicesType_::SizeAtCompileTime,
+    ColsAtCompileTime = IndicesType_::SizeAtCompileTime,
+    MaxRowsAtCompileTime = IndicesType::MaxSizeAtCompileTime,
+    MaxColsAtCompileTime = IndicesType::MaxSizeAtCompileTime,
+    Flags = 0
+  };
+};
+}  // namespace internal
+
+/** \class PermutationWrapper
+ * \ingroup Core_Module
+ *
+ * \brief Class to view a vector of integers as a permutation matrix
+ *
+ * \tparam IndicesType_ the type of the vector of integer (can be any compatible expression)
+ *
+ * This class allows to view any vector expression of integers as a permutation matrix.
+ *
+ * \sa class PermutationBase, class PermutationMatrix
+ */
+template <typename IndicesType_>
+class PermutationWrapper : public PermutationBase<PermutationWrapper<IndicesType_> > {
+  typedef PermutationBase<PermutationWrapper> Base;
+  typedef internal::traits<PermutationWrapper> Traits;
+
+ public:
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  typedef typename Traits::IndicesType IndicesType;
+#endif
+
+  inline PermutationWrapper(const IndicesType& indices) : m_indices(indices) {}
+
+  /** const version of indices(). */
+  const internal::remove_all_t<typename IndicesType::Nested>& indices() const { return m_indices; }
+
+ protected:
+  typename IndicesType::Nested m_indices;
+};
+
+/** \returns the matrix with the permutation applied to the columns.
+ */
+template <typename MatrixDerived, typename PermutationDerived>
+EIGEN_DEVICE_FUNC const Product<MatrixDerived, PermutationDerived, AliasFreeProduct> operator*(
+    const MatrixBase<MatrixDerived>& matrix, const PermutationBase<PermutationDerived>& permutation) {
+  return Product<MatrixDerived, PermutationDerived, AliasFreeProduct>(matrix.derived(), permutation.derived());
+}
+
+/** \returns the matrix with the permutation applied to the rows.
+ */
+template <typename PermutationDerived, typename MatrixDerived>
+EIGEN_DEVICE_FUNC const Product<PermutationDerived, MatrixDerived, AliasFreeProduct> operator*(
+    const PermutationBase<PermutationDerived>& permutation, const MatrixBase<MatrixDerived>& matrix) {
+  return Product<PermutationDerived, MatrixDerived, AliasFreeProduct>(permutation.derived(), matrix.derived());
+}
+
+template <typename PermutationType>
+class InverseImpl<PermutationType, PermutationStorage> : public EigenBase<Inverse<PermutationType> > {
+  typedef typename PermutationType::PlainPermutationType PlainPermutationType;
+  typedef internal::traits<PermutationType> PermTraits;
+
+ protected:
+  InverseImpl() {}
+
+ public:
+  typedef Inverse<PermutationType> InverseType;
+  using EigenBase<Inverse<PermutationType> >::derived;
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  typedef typename PermutationType::DenseMatrixType DenseMatrixType;
+  enum {
+    RowsAtCompileTime = PermTraits::RowsAtCompileTime,
+    ColsAtCompileTime = PermTraits::ColsAtCompileTime,
+    MaxRowsAtCompileTime = PermTraits::MaxRowsAtCompileTime,
+    MaxColsAtCompileTime = PermTraits::MaxColsAtCompileTime
+  };
+#endif
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+  template <typename DenseDerived>
+  void evalTo(MatrixBase<DenseDerived>& other) const {
+    other.setZero();
+    for (Index i = 0; i < derived().rows(); ++i)
+      other.coeffRef(i, derived().nestedExpression().indices().coeff(i)) = typename DenseDerived::Scalar(1);
+  }
+#endif
+
+  /** \return the equivalent permutation matrix */
+  PlainPermutationType eval() const { return derived(); }
+
+  DenseMatrixType toDenseMatrix() const { return derived(); }
+
+  /** \returns the matrix with the inverse permutation applied to the columns.
+   */
+  template <typename OtherDerived>
+  friend const Product<OtherDerived, InverseType, AliasFreeProduct> operator*(const MatrixBase<OtherDerived>& matrix,
+                                                                              const InverseType& trPerm) {
+    return Product<OtherDerived, InverseType, AliasFreeProduct>(matrix.derived(), trPerm.derived());
+  }
+
+  /** \returns the matrix with the inverse permutation applied to the rows.
+   */
+  template <typename OtherDerived>
+  const Product<InverseType, OtherDerived, AliasFreeProduct> operator*(const MatrixBase<OtherDerived>& matrix) const {
+    return Product<InverseType, OtherDerived, AliasFreeProduct>(derived(), matrix.derived());
+  }
+};
+
+template <typename Derived>
+const PermutationWrapper<const Derived> MatrixBase<Derived>::asPermutation() const {
+  return derived();
+}
+
+namespace internal {
+
+template <>
+struct AssignmentKind<DenseShape, PermutationShape> {
+  typedef EigenBase2EigenBase Kind;
+};
+
+}  // end namespace internal
+
+}  // end namespace Eigen
+
+#endif  // EIGEN_PERMUTATIONMATRIX_H