Added the histogram intersection kernel for sparse and dense vectors.

dlib/svm/kernel.h

@@ -400,6 +400,52 @@ namespace dlib
         const linear_kernel<T>& k;
     };
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename T>
+    struct histogram_intersection_kernel
+    {
+        typedef typename T::type scalar_type;
+        typedef T sample_type;
+        typedef typename T::mem_manager_type mem_manager_type;
+
+        scalar_type operator() (
+            const sample_type& a,
+            const sample_type& b
+        ) const
+        { 
+            scalar_type temp = 0;
+            for (long i = 0; i < a.size(); ++i)
+            {
+                temp += std::min(a(i), b(i));
+            }
+            return temp;
+        }
+
+        bool operator== (
+            const histogram_intersection_kernel& 
+        ) const
+        {
+            return true;
+        }
+    };
+
+    template <
+        typename T
+        >
+    void serialize (
+        const histogram_intersection_kernel<T>& ,
+        std::ostream& 
+    ){}
+
+    template <
+        typename T
+        >
+    void deserialize (
+        histogram_intersection_kernel<T>& ,
+        std::istream&  
+    ){}
+
 // ----------------------------------------------------------------------------------------
 
     template <typename T>

dlib/svm/kernel_abstract.h

@@ -422,6 +422,71 @@ namespace dlib
         provides deserialization support for linear_kernel 
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T
+        >
+    struct histogram_intersection_kernel
+    {
+        /*!
+            REQUIREMENTS ON T
+                T must be a dlib::matrix object 
+
+            WHAT THIS OBJECT REPRESENTS
+                This object represents a histogram intersection kernel kernel
+        !*/
+
+        typedef typename T::type scalar_type;
+        typedef T sample_type;
+        typedef typename T::mem_manager_type mem_manager_type;
+
+        scalar_type operator() (
+            const sample_type& a,
+            const sample_type& b
+        ) const;
+        /*!
+            requires
+                - is_vector(a) 
+                - is_vector(b) 
+                - a.size() == b.size()
+                - min(a) >= 0
+                - min(b) >= 0
+            ensures
+                - returns sum over all i: std::min(a(i), b(i)) 
+        !*/
+
+        bool operator== (
+            const histogram_intersection_kernel& k
+        ) const;
+        /*!
+            ensures
+                - returns true
+        !*/
+    };
+
+    template <
+        typename T
+        >
+    void serialize (
+        const histogram_intersection_kernel<T>& item,
+        std::ostream& out
+    );
+    /*!
+        provides serialization support for histogram_intersection_kernel
+    !*/
+
+    template <
+        typename T
+        >
+    void deserialize (
+        histogram_intersection_kernel<T>& item,
+        std::istream& in 
+    );
+    /*!
+        provides deserialization support for histogram_intersection_kernel 
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     template <

dlib/svm/sparse_kernel.h

@@ -311,6 +311,69 @@ namespace dlib
         std::istream& in 
     ){}
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename T>
+    struct sparse_histogram_intersection_kernel
+    {
+        typedef typename T::value_type::second_type scalar_type;
+        typedef T sample_type;
+        typedef default_memory_manager mem_manager_type;
+
+        scalar_type operator() (
+            const sample_type& a,
+            const sample_type& b
+        ) const
+        { 
+            typename sample_type::const_iterator ai = a.begin();
+            typename sample_type::const_iterator bi = b.begin();
+
+            scalar_type sum = 0;
+            while (ai != a.end() && bi != b.end())
+            {
+                if (ai->first == bi->first)
+                {
+                    sum += std::min(ai->second , bi->second);
+                    ++ai;
+                    ++bi;
+                }
+                else if (ai->first < bi->first)
+                {
+                    ++ai;
+                }
+                else 
+                {
+                    ++bi;
+                }
+            }
+
+            return sum;
+        }
+
+        bool operator== (
+            const sparse_histogram_intersection_kernel& 
+        ) const
+        {
+            return true;
+        }
+    };
+
+    template <
+        typename T
+        >
+    void serialize (
+        const sparse_histogram_intersection_kernel<T>& item,
+        std::ostream& out
+    ){}
+
+    template <
+        typename T
+        >
+    void deserialize (
+        sparse_histogram_intersection_kernel<T>& item,
+        std::istream& in 
+    ){}
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/svm/sparse_kernel_abstract.h

@@ -64,8 +64,8 @@ namespace dlib
         ) const;
         /*!
             requires
-                - a contains a sorted range 
-                - b contains a sorted range 
+                - a is a sparse vector
+                - b is a sparse vector
             ensures
                 - returns exp(-gamma * sparse_vector::distance_squared(a,b))
         !*/
@@ -170,8 +170,8 @@ namespace dlib
         ) const;
         /*!
             requires
-                - a contains a sorted range 
-                - b contains a sorted range 
+                - a is a sparse vector
+                - b is a sparse vector
             ensures
                 - returns tanh(gamma * sparse_vector::dot(a,b) + coef)
         !*/
@@ -282,8 +282,8 @@ namespace dlib
         ) const;
         /*!
             requires
-                - a contains a sorted range 
-                - b contains a sorted range 
+                - a is a sparse vector
+                - b is a sparse vector
             ensures
                 - returns pow(gamma * sparse_vector::dot(a,b) + coef, degree)
         !*/
@@ -359,8 +359,8 @@ namespace dlib
         ) const;
         /*!
             requires
-                - a contains a sorted range 
-                - b contains a sorted range 
+                - a is a sparse vector
+                - b is a sparse vector
             ensures
                 - returns sparse_vector::dot(a,b) 
         !*/
@@ -396,6 +396,72 @@ namespace dlib
         provides deserialization support for sparse_linear_kernel 
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T
+        >
+    struct sparse_histogram_intersection_kernel
+    {
+        /*!
+            REQUIREMENTS ON T
+                Must be a sparse vector as defined in dlib/svm/sparse_vector_abstract.h
+
+            WHAT THIS OBJECT REPRESENTS
+                This object represents a histogram intersection kernel 
+                that works with sparse vectors.
+        !*/
+
+        typedef typename T::value_type::second_type scalar_type;
+        typedef T sample_type;
+        typedef default_memory_manager mem_manager_type;
+
+        scalar_type operator() (
+            const sample_type& a,
+            const sample_type& b
+        ) const;
+        /*!
+            requires
+                - a is a sparse vector
+                - b is a sparse vector
+                - all the values in a and b are >= 0
+            ensures
+                - Let A(i) denote the value of the ith dimension of the a vector.
+                - Let B(i) denote the value of the ith dimension of the b vector.
+                - returns sum over all i: std::min(A(i), B(i)) 
+        !*/
+
+        bool operator== (
+            const sparse_histogram_intersection_kernel& k
+        ) const;
+        /*!
+            ensures
+                - returns true
+        !*/
+    };
+
+    template <
+        typename T
+        >
+    void serialize (
+        const sparse_histogram_intersection_kernel<T>& item,
+        std::ostream& out
+    );
+    /*!
+        provides serialization support for sparse_histogram_intersection_kernel
+    !*/
+
+    template <
+        typename T
+        >
+    void deserialize (
+        sparse_histogram_intersection_kernel<T>& item,
+        std::istream& in 
+    );
+    /*!
+        provides deserialization support for sparse_histogram_intersection_kernel 
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
 }