perm_mat.h

#pragma once
 
#include "mat.h"
#include "vec.h"
 
 
namespace cgv {
    namespace math {
struct perm_mat
{
    vec<unsigned> _data;
    
    perm_mat(){}
    
    explicit perm_mat(unsigned n)
    {
        resize(n);
        identity();
    }

    perm_mat(vec<unsigned> p)
    {
        _data = p;
    }

    unsigned size() const 
    {
        return _data.size();
    }

    unsigned nrows() const
    {
        return _data.size();
    }

    unsigned ncols() const
    {
        return _data.size();
    }
 
 
 

    void resize(unsigned n)
    {
        _data.resize(n);
        for(unsigned i = 0; i < n; i++)
            _data[i] = i;
 
    }

    void transpose()
    {
        math::vec<unsigned> temp(_data.size());
        for(unsigned i = 0; i < _data.size(); i++)
            temp[_data[i]] = i;
        _data=temp;
    }
 
    template <typename T>
    operator const mat<T>() const
    {
        mat<T> m;
        m.zeros(size(),size());
 
        for(unsigned i =0; i < size();i++)
            m(i,_data[i])=(T)1.0;
        
        return m;
    }

    perm_mat operator*(const perm_mat& m)
    {
        assert(size() == m.size());
        perm_mat r(size());
        
        for(unsigned i = 0; i < size();i++)
        {
            r(i) = m(operator()(i));
        }
        
        return r;
    }
 
    
 

    void identity()
    {
        for(unsigned i = 0; i < _data.size(); i++)
            _data[i] = i;
    }
 
    //add permutation of the entries i and j
    void swap(unsigned i, unsigned j)
    {
        
        std::swap(_data[i],_data[j]);
    }
 
    unsigned& operator()(unsigned i) 
    {
        return _data[i];
    }
 
 
    unsigned& operator[](unsigned i) 
    {
        return _data[i];
    }
    
    
    unsigned operator()(unsigned i) const
    {
        return _data[i];
    }
 
 
    unsigned operator[](unsigned i) const
    {
        return _data[i];
    }
    
    
 
};
 
 
//multiplies a permutation matrix from left to apply a rows permutation
template<typename T>
mat<T> operator*(const perm_mat& p, const mat<T>& m)
{
    mat<T> r(m.nrows(),m.ncols());
 
    for(unsigned i = 0; i < m.nrows(); i++)
    {
        for(unsigned j = 0; j < m.ncols(); j++)
            r(p(i),j)=m(i,j);
    }
    return r;
}
 
 
 
 
//multiplies a permutation matrix from right to perform a column permutation
template<typename T>
mat<T> operator*(const mat<T>& m, const perm_mat& p)
{
    mat<T> r(m.nrows(),m.ncols());
 
    for(unsigned i = 0; i < m.nrows(); i++)
    {
        for(unsigned j = 0; j < m.ncols(); j++)
            r(i,p(j)) = m(i,j);
    }
    return r;
}
 
 
 
 
 
//multiplies a permutation matrix from left to perform an element permutation on vector v
template<typename T>
vec<T> operator*(const perm_mat& p, const vec<T>& v)
{
    vec<T> r(v.size());
    for(unsigned i = 0; i < v.size(); i++)
    {
    
        r(p[i]) = v(i);
        
    }
    return r;
}
 
 
inline perm_mat transpose(const perm_mat &p)
{
    perm_mat r=p;
    r.transpose();
    return r;
}
 
 
 
 
inline std::ostream& operator<<(std::ostream& out,const  perm_mat& m)
{
    
    for (int i=0;i<(int)m.size();++i)
        out << i << "->"<< m(i)<<"\n";
 
    return out;
}
 
 
 
 
}
 
}