LA_library/permutation.cc

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/*
LA: linear algebra C++ interface library
Copyright (C) 2021 Jiri Pittner <jiri.pittner@jh-inst.cas.cz> or <jiri@pittnerovi.com>
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/>.
*/
#include "permutation.h"
namespace LA {
template <typename T>
void NRPerm<T>::identity()
{
T n=this->size();
#ifdef DEBUG
if(n<0) laerror("invalid permutation size");
#endif
if(n==0) return;
for(T i=1; i<=n; ++i) (*this)[i]=i;
}
template <typename T>
bool NRPerm<T>::is_identity() const
{
T n=this->size();
#ifdef DEBUG
if(n<0) laerror("invalid permutation size");
#endif
if(n==0) return 1;
for(T i=1; i<=n; ++i) if((*this)[i]!=i) return 0;
return 1;
}
template <typename T>
bool NRPerm<T>::is_valid() const
{
T n = this->size();
if(n<0) return 0;
NRVec_from1<T> used(n);
used.clear();
for(T i=1; i<=n; ++i)
{
T x= (*this)[i];
if(x<1||x>n) return 0;
used[x] += 1;
}
for(T i=1; i<=n; ++i) if(used[i]!=1) return 0;
return 1;
}
template <typename T>
NRPerm<T> NRPerm<T>::inverse() const
{
#ifdef DEBUG
if(!this->is_valid()) laerror("inverse of invalid permutation");
#endif
NRPerm<T> q(this->size());
for(T i=1; i<=this->size(); ++i) q[(*this)[i]]=i;
return q;
}
template <typename T>
NRPerm<T> NRPerm<T>::operator*(const NRPerm<T> q) const
{
#ifdef DEBUG
if(!this->is_valid() || !q.is_valid()) laerror("multiplication of invalid permutation");
#endif
T n=this->size();
if(n!=q.size()) laerror("product of incompatible permutations");
NRPerm<T> r(n);
for(T i=1; i<=n; ++i) r[i] = (*this)[q[i]];
return r;
}
template <typename T>
NRPerm<T> NRPerm<T>::conjugate_by(const NRPerm<T> q) const
{
#ifdef DEBUG
if(!this->is_valid() || !q.is_valid()) laerror("multiplication of invalid permutation");
#endif
T n=this->size();
if(n!=q.size()) laerror("product of incompatible permutations");
NRPerm<T> qi=q.inverse();
NRPerm<T> r(n);
for(T i=1; i<=n; ++i) r[i] = qi[(*this)[q[i]]];
return r;
}
template <typename T>
int NRPerm<T>::parity() const
{
if(!this->is_valid()) return 0;
T n=this->size();
if(n==1) return 1;
T count=0;
for(T i=2;i<=n;i++) for(T j=1;j<i;j++) if((*this)[j]>(*this)[i]) count++;
return (count&1)? -1:1;
}
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template <typename T>
NRPerm<T>::NRPerm(const CyclePerm<T> &rhs, int n)
: NRVec_from1<T>(n)
{
#ifdef DEBUG
if(!rhs.is_valid()) laerror("invalid cycle permutation");
#endif
identity();
T ncycles=rhs.size();
for(T j=1; j<=ncycles; ++j)
{
T length= rhs[j].size();
for(T i=1; i<=length; ++i) (*this)[rhs[j][i]] = rhs[j][i%length+1];
}
#ifdef DEBUG
if(!is_valid()) laerror("internal error in NRPerm constructor from CyclePerm");
#endif
}
////////////////////////////////////////////////////////
template <typename T>
CyclePerm<T>:: CyclePerm(const NRPerm<T> &p)
{
#ifdef DEBUG
if(!p.is_valid()) laerror("invalid permutation");
#endif
T n=p.size();
NRVec_from1<T> used(0,n),tmp(n);
T firstunused=1;
T currentcycle=0;
std::list<NRVec<T> > cyclelist={};
do
{
//find a cycle starting with first unused element
T cyclelength=0;
T next = firstunused;
do
{
++cyclelength;
used[next]=1;
tmp[cyclelength] = next;
next = p[next];
}
while(used[next]==0);
if(cyclelength>1) //nontrivial cycle
{
NRVec_from1<T> cycle(&tmp[1],cyclelength);
cyclelist.push_front(cycle);
++currentcycle;
}
while(used[firstunused]) {++firstunused; if(firstunused>n) break;} //find next unused element
}
while(firstunused<=n);
//convert list to NRVec
this->resize(currentcycle);
T i=1;
for(auto l=cyclelist.begin(); l!=cyclelist.end(); ++l) (*this)[i++] = *l;
}
template <typename T>
bool CyclePerm<T>::is_valid() const
{
for(T i=1; i<=this->size(); ++i)
{
T n=(*this)[i].size();
if(n<=0) return false;
for(T j=1; j<=n; ++j)
{
T x=(*this)[i][j];
if(x<=0) return false;
//now check for illegal duplicity of numbers withis a cycle or across cycles
for(T ii=i; ii<=this->size(); ++ii)
{
T nn=(*this)[ii].size();
for(T jj=1; jj<=nn; ++jj)
{
T xx=(*this)[ii][jj];
if(x==xx) return false;
}
}
}
}
return true;
}
template <typename T>
bool CyclePerm<T>::is_identity() const
{
#ifdef DEBUG
if(!this->is_valid()) laerror("operation with an invalid cycleperm");
#endif
for(T i=1; i<=this->size(); ++i) if((*this)[i].size()>1) return false; //at least one nontrivial cycle
return true;
}
template <typename T>
CyclePerm<T> CyclePerm<T>::inverse() const
{
#ifdef DEBUG
if(!this->is_valid()) laerror("operation with an invalid cycleperm");
#endif
CyclePerm<T> r;
T ncycles=this->size();
r.resize(ncycles);
for(T i=1; i<=ncycles; ++i)
{
T length=(*this)[i].size();
r[i].resize(length);
for(T j=1; j<=length; ++j) r[i][j] = (*this)[i][length-j+1];
}
return r;
}
template <typename T>
int CyclePerm<T>::parity() const
{
#ifdef DEBUG
if(!this->is_valid()) laerror("operation with an invalid cycleperm");
#endif
int n_even_cycles=0;
T ncycles=this->size();
for(T i=1; i<=ncycles; ++i)
{
T length=(*this)[i].size();
if((length&1)==0) ++n_even_cycles;
}
return (n_even_cycles&1)?-1:1;
}
template <typename T>
Partition<T> CyclePerm<T>::cycles(const T n) const
{
#ifdef DEBUG
if(!this->is_valid()) laerror("operation with an invalid cycleperm");
#endif
Partition<T> r(n); r.clear();
T ncycles=this->size();
for(T i=1; i<=ncycles; ++i)
{
T length=(*this)[i].size();
if(length<=0||length>n) laerror("unexpected cycle length in permutation");
r[length]++;
}
//fill in trivial cycles of length one
r[1] = n - r.sum();
if(r[1]<0) laerror("inconsistent cycle lengths in CyclePerm::cycles");
return r;
}
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///////////////////////////////////////////////////////
/***************************************************************************//**
* forced instantization in the corresponding object file
******************************************************************************/
template class NRPerm<int>;
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template class CyclePerm<int>;
template class Partition<int>;
}