QpSparseArray.h

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//===========================================================================
/*!
 * 
 *
 * \brief       Special container for certain coefficients describing multi-class SVMs
 * 
 * 
 * 
 *
 * \author      T. Glasmachers
 * \date        2011
 *
 *
 * \par Copyright 1995-2017 Shark Development Team
 * 
 * <BR><HR>
 * This file is part of Shark.
 * <http://shark-ml.org/>
 * 
 * Shark is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published 
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * Shark is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with Shark.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
//===========================================================================


#ifndef SHARK_ALGORITHMS_QP_QPSPARSEARRAY_H
#define SHARK_ALGORITHMS_QP_QPSPARSEARRAY_H


#include <shark/Algorithms/QP/QuadraticProgram.h>
#include <shark/Data/Dataset.h>


namespace shark {


/// \brief specialized container class for multi-class SVM problems
///
/// \par
/// This sparse matrix container allows to explicitly store only those
/// entries of a matrix row that deviate from a row wise default value.
/// This allows for efficient storage of the "kernel modifiers"
/// used to encode dual multi-class support vector machine problems.
template<class QpFloatType>
class QpSparseArray
{
public:
    /// \brief Non-default (non-zero) array entry.
    ///
    /// \par
    /// Data structure describing a non-default
    /// (typically non-zero) entry of a row.
    struct Entry
    {
        std::size_t index;
        QpFloatType value;
    };

    /// \brief Data structure describing a row of the sparse array.
    struct Row
    {
        Entry* entry;
        std::size_t size;
        QpFloatType defaultvalue;
    };

    /// Constructor. The space parameter is an upper limit
    /// on the number of non-default (aka non-zero) entries
    /// of the array.           
    QpSparseArray(
        std::size_t height,
        std::size_t width,
        std::size_t space)
    : m_width(width)
    , m_height(height)
    , m_used(0)
    , m_data(space)
    , m_row(height)
    {
        memset(&m_row[0], 0, height * sizeof(Row));
    }
    
    QpSparseArray(){}

    /// number of columns
    inline std::size_t width() const
    { return m_width; }

    /// number of rows
    inline std::size_t height() const
    { return m_height; }

    /// obtain an element of the matrix
    QpFloatType operator () (std::size_t row, std::size_t col) const
    {
        Row const& r = m_row[row];
        for (std::size_t i=0; i<r.size; i++)
        {
            Entry const& e = r.entry[i];
            if (e.index == col) return e.value;
        }
        return r.defaultvalue;
    }

    /// obtain a row of the matrix
    inline Row const& row(std::size_t row) const
    { return m_row[row]; }

    /// set the default value, that is, the value
    /// of all implicitly defined elements of a row
    inline void setDefaultValue(std::size_t row, QpFloatType defaultvalue)
    { m_row[row].defaultvalue = defaultvalue; }

    /// Set a specific value. Note that entries can not
    /// be changed once they are added, and that adding
    /// elements must be done row-wise, and in order
    /// within each row. However, the order of rows does
    /// not matter.
    void add(std::size_t row, std::size_t col, QpFloatType value)
    {
        SIZE_CHECK(m_used < m_data.size());
    
        Row& r = m_row[row];
        if (r.entry == NULL) r.entry = &m_data[m_used];
        else SIZE_CHECK(r.entry + r.size == &m_data[m_used]);
    
        m_data[m_used].index = col;
        m_data[m_used].value = value;
        m_used++;
        r.size++;
    }
    
    void resize(std::size_t height,std::size_t width,std::size_t space){
        m_width = width;
        m_height = height;
        m_used = 0;
        m_data.resize(space);
        m_row.resize(height);
        memset(&m_row[0], 0, height * sizeof(Row));
    }

protected:
    /// number of columns
    std::size_t m_width;

    /// number of rows
    std::size_t m_height;

    /// current total number of non-default components
    std::size_t m_used;

    /// storage for Entry structures
    std::vector<Entry> m_data;

    /// storage for Row structures
    std::vector<Row> m_row;
};


} // namespace shark
#endif