text: /*
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 3 of the License, or
   * (at your option) any later version.
   *
   * Written (W) 2011 Sergey Lisitsyn
   * Copyright (C) 2011 Berlin Institute of Technology and Max-Planck-Society
   */
  
  #include <shogun/lib/config.h>
  
  #ifndef CAUCHYKERNEL_H_
  #define CAUCHYKERNEL_H_
  
  #include <shogun/lib/common.h>
  #include <shogun/kernel/Kernel.h>
  #include <shogun/distance/Distance.h>
  
  namespace shogun
  {
  
  class CDistance;
  
  /** @brief Cauchy kernel
   *
   * Formally described as
   *
   * \f[
   *		K(x,x') = \frac{1}{1+\frac{\| x-x' \|^2}{\sigma}}
   * \f]
   *
   */
  
  class CCauchyKernel: public CKernel
  {
  public:
  	/** default constructor */
  	CCauchyKernel();
  
  	/** constructor
  	 * @param cache size of cache
  	 * @param sigma kernel parameter sigma
  	 * @param dist distance to be used
  	 */
  	CCauchyKernel(int32_t cache, float64_t sigma, CDistance* dist);
  
  	/** constructor
  	 * @param l features left-side
  	 * @param r features right-side
  	 * @param sigma kernel parameter sigma
  	 * @param dist distance to be used
  	 */
  	CCauchyKernel(CFeatures *l, CFeatures *r, float64_t sigma, CDistance* dist);
  
  	/** initialize kernel with features
  	 * @param l features left-side
  	 * @param r features right-side
  	 * @return true if successful
  	 */
  	virtual bool init(CFeatures* l, CFeatures* r);
  
  	/**
  	 * @return kernel type
  	 */
  	virtual EKernelType get_kernel_type() { return K_CAUCHY; }
  
  	/**
  	 * @return type of features
  	 */
  	virtual EFeatureType get_feature_type() { return m_distance->get_feature_type(); }
  
  	/**
  	 * @return class of features
  	 */
  	virtual EFeatureClass get_feature_class() { return m_distance->get_feature_class(); }
  
  	/**
  	 * @return name of kernel
  	 */
  	virtual const char* get_name() const { return "CauchyKernel"; }
  
  	virtual ~CCauchyKernel();
  
  protected:
  
  	/**
  	 * compute kernel for specific feature vectors
  	 * corresponding to [idx_a] of left-side and [idx_b] of right-side
  	 * @param idx_a left-side index
  	 * @param idx_b right-side index
  	 * @return kernel value
  	 */
  	virtual float64_t compute(int32_t idx_a, int32_t idx_b);
  
  private:
  
  	void init();
  
  protected:
  
  	/// distance to be used
  	CDistance* m_distance;
  
  	/// sigma parameter of kernel
  	float64_t m_sigma;
  
  };
  
  }
  
  #endif /* CAUCHYKERNEL_H_ */
  