/usr/include/shogun/multiclass/ecoc/ECOCRandomSparseEncoder.h is in libshogun-dev 3.1.1-1.
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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) 2012 Chiyuan Zhang
* Copyright (C) 2012 Chiyuan Zhang
*/
#ifndef ECOCRANDOMSPARSEENCODER_H__
#define ECOCRANDOMSPARSEENCODER_H__
#include <shogun/mathematics/Math.h>
#include <shogun/multiclass/ecoc/ECOCEncoder.h>
namespace shogun
{
/** ECOC Random Sparse Encoder.
*
* Given probabilities P(0), P(+1) and P(-1) (that sums to 1), the codebook element is randomly
* selected according to those probabilities. However, to avoid generating invalid code (i.e. not
* both +1 and -1 are present), we use a heuristic modification here:
*
* 1. randomly select two positions and assign them (+1,-1) or (-1,+1) with probability 0.5, 0.5 respectively
* 2. random sample and assign values to the rest of the code positions
*
* In this way, we guarantee that both +1 and -1 are present in the code. However, the effective probability
* is changed to Q. Assume number of classes is K, then
*
* * Q(0) = (K-2)/K * P(0)
* * Q(+1) = 1/K + (K-2)/K * P(+1)
* * Q(-1) = 1/K + (K-2)/K * P(-1)
*/
class CECOCRandomSparseEncoder: public CECOCEncoder
{
public:
/** constructor
* @param maxiter max number of iterations
* @param codelen code length, if set to zero, will be computed automatically via get_default_code_length
* @param pzero probability of zero
* @param pposone probability of +1
* @param pnegone probability of -1
*
* @see get_default_code_length
*/
CECOCRandomSparseEncoder(int32_t maxiter=10000, int32_t codelen=0,
float64_t pzero=0.5, float64_t pposone=0.25, float64_t pnegone=0.25);
/** destructor */
virtual ~CECOCRandomSparseEncoder() {}
/** set probability
* @param pzero probability of zero
* @param pposone probability of +1
* @param pnegone probability of -1
*/
void set_probability(float64_t pzero, float64_t pposone, float64_t pnegone);
/** get name */
virtual const char* get_name() const { return "ECOCRandomSparseEncoder"; }
/** get default code length
* @param num_classes number of classes
*
* In Sparse Random Coding, 15 * log(num_classes) is suggested as code length.
* See
*
* S. Escalera, O. Pujol, and P. Radeva. Separability of ternary codes for sparse designs
* of error-correcting output codes. Pattern Recognition Letters, 30:285-297, 2009.
*/
int32_t get_default_code_length(int32_t num_classes) const
{
return static_cast<int32_t>(CMath::round(15 * CMath::log(num_classes)));
}
/** init codebook.
* @param num_classes number of classes in this problem
*/
virtual SGMatrix<int32_t> create_codebook(int32_t num_classes);
protected:
/** maximum number of iterations */
int32_t m_maxiter;
/** code length */
int32_t m_codelen;
/** probability of zero */
float64_t m_pzero;
/** probability of +1 */
float64_t m_pposone;
/** probability of -1 */
float64_t m_pnegone;
private:
/** ensure probability sum to one
* @param pzero probability of zero
* @param pposone probability of +1
* @param pnegone probability of -1
*/
bool check_probability(float64_t pzero, float64_t pposone, float64_t pnegone)
{
if (CMath::abs(pzero + pposone + pnegone - 1) > 1e-5)
return false;
return true;
}
/** init parameters */
void init();
};
} /* shogun */
#endif /* end of include guard: ECOCRANDOMSPARSEENCODER_H__ */
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