PermMatrix.h

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// Copyright (C) 2008-2025 The Octave Project Developers
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#if ! defined (octave_PermMatrix_h)
#define octave_PermMatrix_h 1
 
#include "octave-config.h"
 
#include "Array.h"
#include "mx-defs.h"
 
// Array<T> is inherited privately so that some methods, like index, don't
// produce unexpected results.
 
class OCTAVE_API PermMatrix : protected Array<octave_idx_type>
{
public:
 
  PermMatrix () = default;
 
  PermMatrix (const PermMatrix& m) = default;
 
  PermMatrix& operator = (const PermMatrix& m) = default;
 
  ~PermMatrix () = default;
 
  OCTAVE_API PermMatrix (octave_idx_type n);
 
  OCTAVE_API PermMatrix (const Array<octave_idx_type>& p, bool colp,
                         bool check = true);
 
  OCTAVE_API PermMatrix (const octave::idx_vector& idx, bool colp,
                         octave_idx_type n = 0);
 
  octave_idx_type dim1 () const
  { return Array<octave_idx_type>::numel (); }
  octave_idx_type dim2 () const
  { return Array<octave_idx_type>::numel (); }
 
  octave_idx_type rows () const { return dim1 (); }
  octave_idx_type cols () const { return dim2 (); }
  octave_idx_type columns () const { return dim2 (); }
 
  octave_idx_type perm_length () const
  { return Array<octave_idx_type>::numel (); }
  // FIXME: a dangerous ambiguity?
  octave_idx_type length () const
  { return perm_length (); }
 
  octave_idx_type numel () const { return dim1 () * dim2 (); }
 
  std::size_t byte_size () const
  { return Array<octave_idx_type>::byte_size (); }
 
  dim_vector dims () const { return dim_vector (dim1 (), dim2 ()); }
 
  bool isempty () const { return numel () == 0; }
 
  int ndims () const { return 2; }
 
  const Array<octave_idx_type>& col_perm_vec () const
  { return *this; }
 
  octave_idx_type
  elem (octave_idx_type i, octave_idx_type j) const
  {
    return (Array<octave_idx_type>::elem (j) == i) ? 1 : 0;
  }
 
  octave_idx_type
  checkelem (octave_idx_type i, octave_idx_type j) const;
 
  octave_idx_type
  operator () (octave_idx_type i, octave_idx_type j) const
  {
    return elem (i, j);
  }
 
  // These are, in fact, super-fast.
  OCTAVE_API PermMatrix transpose () const;
  OCTAVE_API PermMatrix inverse () const;
 
  // Determinant, i.e., the sign of permutation.
  OCTAVE_API octave_idx_type determinant () const;
 
  // Efficient integer power of a permutation.
  OCTAVE_API PermMatrix power (octave_idx_type n) const;
 
  bool is_col_perm () const { return true; }
  bool is_row_perm () const { return false; }
 
  void print_info (std::ostream& os, const std::string& prefix) const
  { Array<octave_idx_type>::print_info (os, prefix); }
 
  static OCTAVE_API PermMatrix eye (octave_idx_type n);
 
private:
 
  PermMatrix pos_power (octave_idx_type m) const;
 
  void setup (const Array<octave_idx_type>& p, bool colp, bool check);
 
  void setup (const octave::idx_vector& idx, bool colp, octave_idx_type n);
};
 
// Multiplying permutations together.
OCTAVE_API PermMatrix
operator * (const PermMatrix& a, const PermMatrix& b);
 
#endif