text: /*
   * Copyright (c) The Shogun Machine Learning Toolbox
   * Written (w) 2015 Wu Lin
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice, this
   *    list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
   * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * The views and conclusions contained in the software and documentation are those
   * of the authors and should not be interpreted as representing official policies,
   * either expressed or implied, of the Shogun Development Team.
   *
   */
  
  #ifndef PENALTY_H
  #define PENALTY_H
  #include <shogun/base/SGObject.h>
  #include <shogun/lib/config.h>
  namespace shogun
  {
  /** @brief The base class for penalty/regularization used in minimization.
   *
   * This is the interface of regularizers used in minimizers.
   * (eg,
   * FirstOrderMinimizer::update_gradient(SGVector<float64_t> gradient, SGVector<float64_t> var)
   * FirstOrderMinimizer::get_penalty(SGVector<float64_t> var)
   * ) 
   *
   */
  class Penalty:public CSGObject
  {
  public:
  	virtual ~Penalty() {};
  
  	/** Given the value of a target variable,
  	 * this method returns the penalty of the variable 
  	 *
  	 * For L2 penalty, \f$L2(w)\f$
  	 * \f[
  	 * L2(w)=\frac{w^t w}{2}
  	 * \f]
  	 *
  	 * @param variable value of the variable
  	 * @return penalty of the variable
  	 */
  	virtual float64_t get_penalty(float64_t variable)=0;
  
  	/** Returns the gradient of the penalty wrt a target variable
  	 * Note that the penalized gradient=unpenalized gradient+penalty_gradient
  	 *
  	 * For L2 penalty
  	 * \f[
  	 * \frac{\partial L2(w) }{\partial w}=w
  	 * \f]
  	 *
  	 * @param variable value of a target variable
  	 * @param gradient unregularized/unpenalized gradient of the variable
  	 * @return the gradient of the penalty wrt the variable
  	 */
  	virtual float64_t get_penalty_gradient(float64_t variable,
  		float64_t gradient)=0;
  
  };
  
  }
  #endif
  