SparsePolyFeatures.cpp

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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) 2010 Soeren Sonnenburg
 * Copyright (C) 2010 Berlin Institute of Technology
 */
#include "features/SparsePolyFeatures.h"
#include "lib/Hash.h"

using namespace shogun;

CSparsePolyFeatures::CSparsePolyFeatures(CSparseFeatures<float64_t>* feat, int32_t degree, bool normalize, int32_t hash_bits)
    : CDotFeatures(), m_normalization_values(NULL)
{
    ASSERT(feat);

    m_feat = feat;
    SG_REF(m_feat);
    m_degree=degree;
    m_normalize=normalize;
    m_hash_bits=hash_bits;
    mask=(uint32_t) (((uint64_t) 1)<<m_hash_bits)-1;
    m_output_dimensions=1<<m_hash_bits;
    m_input_dimensions=feat->get_num_features();

    if (m_normalize)
        store_normalization_values();
}

CSparsePolyFeatures::~CSparsePolyFeatures()
{
    delete[] m_normalization_values;
    SG_UNREF(m_feat);
}

float64_t CSparsePolyFeatures::dot(int32_t vec_idx1, int32_t vec_idx2)
{

    int32_t len1, len2;
    bool do_free1, do_free2;
    TSparseEntry<float64_t>* vec1 = m_feat->get_sparse_feature_vector(vec_idx1, len1, do_free1);
    TSparseEntry<float64_t>* vec2 = m_feat->get_sparse_feature_vector(vec_idx2, len2, do_free2);

    float64_t result=CSparseFeatures<float64_t>::sparse_dot(1, vec1, len1, vec2, len2);
    result=CMath::pow(result, m_degree);

    m_feat->free_feature_vector(vec1, len1, do_free1);
    m_feat->free_feature_vector(vec2, len2, do_free2);

    return result;
}

float64_t CSparsePolyFeatures::dense_dot(int32_t vec_idx1, float64_t* vec2, int32_t vec2_len)
{
    if (vec2_len != m_output_dimensions)
        SG_ERROR("Dimensions don't match, vec2_dim=%d, m_output_dimensions=%d\n", vec2_len, m_output_dimensions);

    int32_t vlen;
    bool do_free;
    TSparseEntry<float64_t>* vec = m_feat->get_sparse_feature_vector(vec_idx1, vlen, do_free);

    float64_t result=0;

    if (vec)
    {
        if (m_degree==2)
        {
            /* (a+b)^2 = a^2 + 2ab +b^2 */
            for (int32_t i=0; i<vlen; i++)
            {
                float64_t v1=vec[i].entry;
                uint32_t seed=CHash::MurmurHash2((uint8_t*) &(vec[i].feat_index), sizeof(int32_t), 0xDEADBEAF);

                for (int32_t j=i; j<vlen; j++)
                {
                    float64_t v2=vec[j].entry;
                    uint32_t h=CHash::MurmurHash2((uint8_t*) &(vec[j].feat_index), sizeof(int32_t), seed) & mask;
                    float64_t v;

                    if (i==j)
                        v=v1*v1;
                    else
                        v=CMath::sqrt(2.0)*v1*v2;

                    result+=v*vec2[h];
                }
            }
        }
        else if (m_degree==3)
            SG_NOTIMPLEMENTED;
    }
    
    if (m_normalize)
        result/=m_normalization_values[vec_idx1];

    m_feat->free_feature_vector(vec, vlen, do_free);
    return result;
}

void CSparsePolyFeatures::add_to_dense_vec(float64_t alpha, int32_t vec_idx1, float64_t* vec2, int32_t vec2_len, bool abs_val)
{
    if (vec2_len != m_output_dimensions)
        SG_ERROR("Dimensions don't match, vec2_dim=%d, m_output_dimensions=%d\n", vec2_len, m_output_dimensions);

    int32_t vlen;
    bool do_free;
    TSparseEntry<float64_t>* vec = m_feat->get_sparse_feature_vector(vec_idx1, vlen, do_free);

    float64_t norm_val=1.0;
    if (m_normalize)
        norm_val = m_normalization_values[vec_idx1];
    alpha/=norm_val;

    if (m_degree==2)
    {
        /* (a+b)^2 = a^2 + 2ab +b^2 */
        for (int32_t i=0; i<vlen; i++)
        {
            float64_t v1=vec[i].entry;
            uint32_t seed=CHash::MurmurHash2((uint8_t*) &(vec[i].feat_index), sizeof(int32_t), 0xDEADBEAF);

            for (int32_t j=i; j<vlen; j++)
            {
                float64_t v2=vec[j].entry;
                uint32_t h=CHash::MurmurHash2((uint8_t*) &(vec[j].feat_index), sizeof(int32_t), seed) & mask;
                float64_t v;

                if (i==j)
                    v=alpha*v1*v1;
                else
                    v=alpha*CMath::sqrt(2.0)*v1*v2;

                if (abs_val)
                    vec2[h]+=CMath::abs(v); 
                else
                    vec2[h]+=v; 
            }
        }
    }
    else if (m_degree==3)
        SG_NOTIMPLEMENTED;

    m_feat->free_feature_vector(vec, vlen, do_free);
}

void CSparsePolyFeatures::store_normalization_values()
{
    delete[] m_normalization_values;

    int32_t num_vec = this->get_num_vectors();

    m_normalization_values=new float64_t[num_vec];
    for (int i=0; i<num_vec; i++)
    {
        float64_t val = CMath::sqrt(dot(i,i)); 
        if (val==0)
            // trap division by zero
            m_normalization_values[i]=1.0;
        else 
            m_normalization_values[i]=val;
    }
        
}

CFeatures* CSparsePolyFeatures::duplicate() const
{
    return new CSparsePolyFeatures(*this);
}