```// Copyright (C) 2010  Davis E. King (davis@dlib.net)
#undef DLIB_MR_FUNCTION_ObJECTS_ABSTRACT_H__
#ifdef DLIB_MR_FUNCTION_ObJECTS_ABSTRACT_H__

#include "../matrix.h"
#include <cmath>

namespace dlib
{

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

struct squared_euclidean_distance
{
/*!
WHAT THIS OBJECT REPRESENTS
This is a simple function object that computes squared euclidean distance
between two dlib::matrix objects.
!*/

squared_euclidean_distance (
);
/*!
ensures
- #lower == 0
- #upper == std::numeric_limits<double>::infinity()
!*/

squared_euclidean_distance (
const double l,
const double u
);
/*!
ensures
- #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;
/*!
requires
- sample_type should be a kind of dlib::matrix
ensures
- let LEN = length_squared(a-b)
- if (lower <= LEN <= upper) then
- returns LEN
- else
- returns std::numeric_limits<double>::infinity()
!*/
};

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

struct use_weights_of_one
{
/*!
WHAT THIS OBJECT REPRESENTS
This is a simple function object that takes a single argument
and always returns 1
!*/

template <typename edge_type>
double operator() (
const edge_type&
) const;
/*!
ensures
- returns 1
!*/
};

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

struct use_gaussian_weights
{
/*!
WHAT THIS OBJECT REPRESENTS
This is a simple function object that takes a single argument
which should be an object similar to dlib::sample_pair.
!*/

use_gaussian_weights (
);
/*!
ensures
- #gamma == 0.1
!*/

use_gaussian_weights (
double g
);
/*!
ensures
- #gamma == g
!*/

double gamma;

template <typename edge_type>
double operator() (
const edge_type& e
) const;
/*!
requires
- e.distance() must be a valid expression that returns a number
(e.g. edge_type might be dlib::sample_pair)
ensures
- returns std::exp(-gamma*e.distance());
!*/
};

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

}

#endif // DLIB_MR_FUNCTION_ObJECTS_ABSTRACT_H__

```