```// Copyright (C) 2010  Davis E. King (davis@dlib.net)
#ifndef DLIB_MR_FUNCTION_ObJECTS_Hh_
#define DLIB_MR_FUNCTION_ObJECTS_Hh_

#include "function_objects_abstract.h"
#include "../matrix.h"
#include "../svm/sparse_vector.h"
#include <cmath>
#include <limits>

namespace dlib
{

// ----------------------------------------------------------------------------------------

struct squared_euclidean_distance
{
squared_euclidean_distance (
) :
lower(0),
upper(std::numeric_limits<double>::infinity())
{}

squared_euclidean_distance (
const double l,
const double u
) :
lower(l),
upper(u)
{}

const double lower;
const double upper;

template <typename sample_type>
double operator() (
const sample_type& a,
const sample_type& b
) const
{
const double len = length_squared(a-b);
if (lower <= len && len <= upper)
return len;
else
return std::numeric_limits<double>::infinity();
}
};

// ----------------------------------------------------------------------------------------

struct cosine_distance
{
template <typename sample_type>
double operator() (
const sample_type& a,
const sample_type& b
) const
{
const double temp = length(a)*length(b);
if (temp == 0)
return 0;
else
return 1-dot(a,b)/temp;
}
};

// ----------------------------------------------------------------------------------------

struct negative_dot_product_distance
{
template <typename sample_type>
double operator() (
const sample_type& a,
const sample_type& b
) const
{
return -dot(a,b);
}
};

// ----------------------------------------------------------------------------------------

struct use_weights_of_one
{
template <typename edge_type>
double operator() (
const edge_type&
) const
{
return 1;
}
};

// ----------------------------------------------------------------------------------------

struct use_gaussian_weights
{
use_gaussian_weights (
)
{
gamma = 0.1;
}

use_gaussian_weights (
double g
)
{
gamma = g;
}

double gamma;

template <typename edge_type>
double operator() (
const edge_type& e
) const
{
return std::exp(-gamma*e.distance());
}
};

// ----------------------------------------------------------------------------------------

}

#endif // DLIB_MR_FUNCTION_ObJECTS_Hh_

```