SigmoidKernel.h

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/*
 * 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) 1999-2010 Soeren Sonnenburg
 * Copyright (C) 1999-2009 Fraunhofer Institute FIRST and Max-Planck-Society
 * Copyright (C) 2010 Berlin Institute of Technology
 */

#ifndef _SIGMOIDKERNEL_H___
#define _SIGMOIDKERNEL_H___

#include <shogun/lib/common.h>
#include <shogun/kernel/DotKernel.h>
#include <shogun/features/DotFeatures.h>

namespace shogun
{
class CSigmoidKernel: public CDotKernel
{
    public:
        CSigmoidKernel();

        CSigmoidKernel(int32_t size, float64_t gamma, float64_t coef0);

        CSigmoidKernel(CDotFeatures* l, CDotFeatures* r, int32_t size,
            float64_t gamma, float64_t coef0);

        virtual ~CSigmoidKernel();

        virtual bool init(CFeatures* l, CFeatures* r);

        virtual void cleanup();

        virtual EKernelType get_kernel_type() { return K_SIGMOID; }

        virtual const char* get_name() const { return "SigmoidKernel"; }

    protected:
        virtual float64_t compute(int32_t idx_a, int32_t idx_b)
        {
            return tanh(gamma*CDotKernel::compute(idx_a,idx_b)+coef0);
        }

    private:
        void init();

    protected:
        float64_t gamma;
        float64_t coef0;
};
}
#endif /* _SIGMOIDKERNEL_H__ */