Added overloads of the kernel_derivative object for all the kernels in dlib.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403067

dlib/svm/kernel.h

@@ -318,6 +318,28 @@ namespace dlib
         }
     }
 
+    template <
+        typename T 
+        >
+    struct kernel_derivative<sigmoid_kernel<T> >
+    {
+        typedef typename T::type scalar_type;
+        typedef T sample_type;
+        typedef typename T::mem_manager_type mem_manager_type;
+
+        kernel_derivative(const sigmoid_kernel<T>& k_) : k(k_){}
+
+        const sample_type& operator() (const sample_type& x, const sample_type& y) const
+        {
+            // return the derivative of the rbf kernel
+            temp = k.gamma*x*(1-std::pow(k(x,y),2));
+            return temp;
+        }
+
+        const sigmoid_kernel<T>& k;
+        mutable sample_type temp;
+    };
+
 // ----------------------------------------------------------------------------------------
 
     template <typename T>
@@ -359,6 +381,25 @@ namespace dlib
         std::istream& in 
     ){}
 
+    template <
+        typename T 
+        >
+    struct kernel_derivative<linear_kernel<T> >
+    {
+        typedef typename T::type scalar_type;
+        typedef T sample_type;
+        typedef typename T::mem_manager_type mem_manager_type;
+
+        kernel_derivative(const linear_kernel<T>& k_) : k(k_){}
+
+        const sample_type& operator() (const sample_type& x, const sample_type& y) const
+        {
+            return x;
+        }
+
+        const linear_kernel<T>& k;
+    };
+
 // ----------------------------------------------------------------------------------------
 
     template <typename T>
@@ -442,6 +483,25 @@ namespace dlib
         }
     }
 
+    template <
+        typename T 
+        >
+    struct kernel_derivative<offset_kernel<T> >
+    {
+        typedef typename T::scalar_type scalar_type;
+        typedef typename T::sample_type sample_type;
+        typedef typename T::mem_manager_type mem_manager_type;
+
+        kernel_derivative(const offset_kernel<T>& k) : der(k.kernel){}
+
+        const sample_type operator() (const sample_type& x, const sample_type& y) const
+        {
+            return der(x,y);
+        }
+
+        kernel_derivative<T> der;
+    };
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/svm/kernel_abstract.h

@@ -537,6 +537,9 @@ namespace dlib
                 kernel_type must be one of the following kernel types:
                     - radial_basis_kernel
                     - polynomial_kernel 
+                    - sigmoid_kernel
+                    - linear_kernel
+                    - offset_kernel
 
             WHAT THIS OBJECT REPRESENTS
                 This is a function object that computes the derivative of a kernel 
@@ -562,7 +565,7 @@ namespace dlib
         ) const;
         /*!
             ensures
-                - returns the derivative of k with respect to y.  Or in other words, k(x, y+dy)/dy 
+                - returns the derivative of k with respect to y.  
         !*/
 
         const kernel_type& k;

dlib/test/svm.cpp

@@ -399,9 +399,60 @@ namespace
 
 // ----------------------------------------------------------------------------------------
 
+    template <typename kernel_type>
+    struct kernel_der_obj
+    {
+        typename kernel_type::sample_type x;
+        kernel_type k;
+
+        double operator()(const typename kernel_type::sample_type& y) const { return k(x,y); }
+    };
 
 
+    template <typename kernel_type>
+    void test_kernel_derivative (
+        const kernel_type& k,
+        const typename kernel_type::sample_type& x, 
+        const typename kernel_type::sample_type& y 
+    )
+    {
+        kernel_der_obj<kernel_type> obj;
+        obj.x = x;
+        obj.k = k;
+        kernel_derivative<kernel_type> der(obj.k);
+        DLIB_CASSERT(dlib::equal(derivative(obj)(y) , der(obj.x,y), 1e-5), "");
+    }
 
+    void test_kernel_derivative (
+    )
+    {
+        typedef matrix<double, 2, 1> sample_type;
+
+        sigmoid_kernel<sample_type> k1;
+        radial_basis_kernel<sample_type> k2;
+        linear_kernel<sample_type> k3;
+        polynomial_kernel<sample_type> k4(2,3,4);
+
+        offset_kernel<sigmoid_kernel<sample_type> > k5;
+        offset_kernel<radial_basis_kernel<sample_type> > k6;
+
+        dlib::rand::float_1a rnd;
+
+        sample_type x, y;
+        for (int i = 0; i < 10; ++i)
+        {
+            x = randm(2,1,rnd);
+            y = randm(2,1,rnd);
+            test_kernel_derivative(k1, x, y);
+            test_kernel_derivative(k2, x, y);
+            test_kernel_derivative(k3, x, y);
+            test_kernel_derivative(k4, x, y);
+            test_kernel_derivative(k5, x, y);
+            test_kernel_derivative(k6, x, y);
+        }
+    }
+
+// ----------------------------------------------------------------------------------------
 
     class svm_tester : public tester
     {
@@ -415,6 +466,7 @@ namespace
         void perform_test (
         )
         {
+            test_kernel_derivative();
             test_binary_classification();
             test_clutering();
             test_regression();