CGII/framework/include/cgv/math/perm_mat.h

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2018-05-17 14:01:02 +00:00
#pragma once
#include "mat.h"
#include "vec.h"
namespace cgv {
namespace math {
/**
* a permutation matrix type
*/
struct perm_mat
{
///internal storage of the permutation
vec<unsigned> _data;
///standard constructor
perm_mat(){}
///create an nxn identity permutation matrix (storage is only n)
explicit perm_mat(unsigned n)
{
resize(n);
identity();
}
///creates a permutation from a given permutation vector
perm_mat(vec<unsigned> p)
{
_data = p;
}
///number of stored elements
unsigned size() const
{
return _data.size();
}
///number of rows
unsigned nrows() const
{
return _data.size();
}
///number of rows
unsigned ncols() const
{
return _data.size();
}
///resize the permutation matrix
void resize(unsigned n)
{
_data.resize(n);
for(unsigned i = 0; i < n; i++)
_data[i] = i;
}
///compute the transpose permutation matrix (equal to inverse permutation)
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;
}
///product with another permutation matrix
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;
}
///set to identity matrix
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;
}
}
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}