view liboctave/array/PermMatrix.cc @ 30564:796f54d4ddbf stable

update Octave Project Developers copyright for the new year In files that have the "Octave Project Developers" copyright notice, update for 2021. In all .txi and .texi files except gpl.txi and gpl.texi in the doc/liboctave and doc/interpreter directories, change the copyright to "Octave Project Developers", the same as used for other source files. Update copyright notices for 2022 (not done since 2019). For gpl.txi and gpl.texi, change the copyright notice to be "Free Software Foundation, Inc." and leave the date at 2007 only because this file only contains the text of the GPL, not anything created by the Octave Project Developers. Add Paul Thomas to contributors.in.
author John W. Eaton <jwe@octave.org>
date Tue, 28 Dec 2021 18:22:40 -0500
parents 29a1f8fd8ee6
children 597f3ee61a48
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////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2008-2022 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
//
// Octave 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.
//
// Octave 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 Octave; see the file COPYING.  If not, see
// <https://www.gnu.org/licenses/>.
//
////////////////////////////////////////////////////////////////////////

#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif

#include "PermMatrix.h"
#include "idx-vector.h"
#include "Array-util.h"
#include "oct-locbuf.h"

OCTAVE_NORETURN static
void
err_invalid_permutation (void)
{
  (*current_liboctave_error_handler) ("PermMatrix: invalid permutation vector");
}

void
PermMatrix::setup (const Array<octave_idx_type>& p, bool colp, bool check)
{
  if (check)
    {
      if (! octave::idx_vector (p).is_permutation (p.numel ()))
        err_invalid_permutation ();
    }

  if (! colp)
    *this = this->transpose ();
}

PermMatrix::PermMatrix (const Array<octave_idx_type>& p, bool colp, bool check)
  : Array<octave_idx_type> (p)
{
  setup (p, colp, check);
}

void
PermMatrix::setup (const octave::idx_vector& idx, bool colp, octave_idx_type n)
{
  octave_idx_type len = idx.length (n);

  if (! idx.is_permutation (len))
    err_invalid_permutation ();

  Array<octave_idx_type> idxa (dim_vector (len, 1));
  for (octave_idx_type i = 0; i < len; i++) idxa(i) = idx(i);
  Array<octave_idx_type>::operator = (idxa);

  if (! colp)
    *this = this->transpose ();
}

PermMatrix::PermMatrix (const octave::idx_vector& idx, bool colp, octave_idx_type n)
  : Array<octave_idx_type> ()
{
  setup (idx, colp, n);
}

PermMatrix::PermMatrix (octave_idx_type n)
  : Array<octave_idx_type> (dim_vector (n, 1))
{
  for (octave_idx_type i = 0; i < n; i++)
    xelem (i) = i;
}

octave_idx_type
PermMatrix::checkelem (octave_idx_type i, octave_idx_type j) const
{
  octave_idx_type len = Array<octave_idx_type>::numel ();
  if (i < 0 || j < 0 || i > len || j > len)
    (*current_liboctave_error_handler) ("index out of range");

  return elem (i, j);
}

PermMatrix
PermMatrix::transpose (void) const
{
  octave_idx_type len = Array<octave_idx_type>::numel ();

  PermMatrix retval (len);

  for (octave_idx_type i = 0; i < len; ++i)
    retval.xelem (xelem (i)) = i;

  return retval;
}

PermMatrix
PermMatrix::inverse (void) const
{
  return transpose ();
}

octave_idx_type
PermMatrix::determinant (void) const
{
  // Determine the sign of a permutation in linear time.
  // Is this widely known?

  octave_idx_type len = perm_length ();
  const octave_idx_type *pa = data ();

  OCTAVE_LOCAL_BUFFER (octave_idx_type, p, len);
  OCTAVE_LOCAL_BUFFER (octave_idx_type, q, len);

  for (octave_idx_type i = 0; i < len; i++)
    {
      p[i] = pa[i];
      q[p[i]] = i;
    }

  bool neg = false;

  for (octave_idx_type i = 0; i < len; i++)
    {
      octave_idx_type j = p[i];
      octave_idx_type k = q[i];
      if (j != i)
        {
          p[k] = p[i];
          q[j] = q[i];
          neg = ! neg;
        }
    }

  return neg ? -1 : 1;
}

PermMatrix
PermMatrix::power(octave_idx_type m) const
{
  if (m < 0)
    return inverse ().pos_power (-m);
  else if (m > 0)
    return pos_power (m);
  else
    return PermMatrix (rows ());
}

PermMatrix
PermMatrix::pos_power (octave_idx_type m) const
{
  octave_idx_type n = rows ();

  const octave_idx_type *p = data ();
  Array<octave_idx_type> res_pvec (dim_vector (n, 1), -1);
  octave_idx_type *q = res_pvec.fortran_vec ();

  for (octave_idx_type ics = 0; ics < n; ics++)
    {
      if (q[ics] > 0)
        continue;

      // go forward m steps or until a cycle is found.
      octave_idx_type ic, j;
      for (j = 1, ic = p[ics]; j != m && ic != ics; j++, ic = p[ic]) ;
      if (ic == ics)
        {
          // reduce power.
          octave_idx_type mm = m % j;
          // go forward mm steps.
          for (j = 0, ic = ics; j != mm; j++, ic = p[ic]) ;
        }

      // now ic = p^m[ics].  Loop through the whole cycle.
      octave_idx_type jcs = ics;
      do
        {
          q[jcs] = ic;
          jcs = p[jcs]; ic = p[ic];
        }
      while (jcs != ics);

    }

  return PermMatrix (res_pvec, true, false);
}

PermMatrix
PermMatrix::eye (octave_idx_type n)
{
  return PermMatrix (n);
}

PermMatrix
operator *(const PermMatrix& a, const PermMatrix& b)
{
  PermMatrix r;

  const Array<octave_idx_type> ia = a.col_perm_vec ();
  const Array<octave_idx_type> ib = b.col_perm_vec ();

  octave_idx_type n = a.columns ();

  if (n != b.rows ())
    octave::err_nonconformant ("operator *", n, n, b.rows (), b.rows ());

  r = PermMatrix (ia.index (octave::idx_vector (ib)), true, false);

  return r;
}