Corrected a mistake in CHI2 kernel in line 354 and line 362 svm.cpp

Added new kernels to documentation

modules/ml/doc/support_vector_machines.rst

@@ -115,9 +115,13 @@ The constructors.
 
         * **CvSVM::SIGMOID** Sigmoid kernel: :math:`K(x_i, x_j) = \tanh(\gamma x_i^T x_j + coef0)`.
 
+        * **CvSVM::CHI2** Exponential Chi2 kernel, similar to the RBF kernel: :math:`K(x_i, x_j) = e^{-\gamma \chi^2(x_i,x_j)}, \chi^2(x_i,x_j) = (x_i-x_j)^2/(x_i+x_j), \gamma > 0`.
+
+        * **CvSVM::INTER** Histogram intersection kernel. A fast kernel. :math:`K(x_i, x_j) = min(x_i,x_j)`.
+
     :param degree: Parameter ``degree`` of a kernel function (POLY).
 
-    :param gamma: Parameter :math:`\gamma` of a kernel function (POLY / RBF / SIGMOID).
+    :param gamma: Parameter :math:`\gamma` of a kernel function (POLY / RBF / SIGMOID / CHI2).
 
     :param coef0: Parameter ``coef0`` of a kernel function (POLY / SIGMOID).
 
@@ -142,6 +146,10 @@ The default constructor initialize the structure with following values:
         term_crit = cvTermCriteria( CV_TERMCRIT_ITER+CV_TERMCRIT_EPS, 1000, FLT_EPSILON );
     }
 
+A comparison of different kernels on the following 2D test case with four classes. Four C_SVC SVMs have been trained (one against rest) with auto_train. Evaluation on three different kernels (CHI2, INTER, RBF). The color depicts the class with max score. Bright means max-score > 0, dark means max-score < 0.
+
+.. image:: pics/SVM_Comparison.png
+
 
 
 CvSVM

modules/ml/src/svm.cpp

@@ -351,7 +351,7 @@ void CvSVMKernel::calc_chi2( int vcount, int var_count, const float** vecs,
         double chi2 = 0;
         for(k = 0 ; k < var_count; k++ ) 
 	{
-            double d = sample[k]*another[k];
+            double d = sample[k]-another[k];
 	    double devisor = sample[k]+another[k];
 	    /// if devisor == 0, the Chi2 distance would be zero, but calculation would rise an error because of deviding by zero
 	    if (devisor != 0) 
@@ -359,7 +359,7 @@ void CvSVMKernel::calc_chi2( int vcount, int var_count, const float** vecs,
 	      chi2 += d*d/devisor;
 	    } 
 	}
-        results[j] = (Qfloat) (gamma*(1.0-2*chi2));
+        results[j] = (Qfloat) (gamma*chi2);
     } 
     if( vcount > 0 )
       cvExp( &R, &R );