opencv/modules/ml/src/gbt.cpp

#include "precomp.hpp"
#include <string>
#include <time.h>

using namespace std;

#define pCvSeq CvSeq*
#define pCvDTreeNode CvDTreeNode*

#define CV_CMP_FLOAT(a,b) ((a) < (b))
static CV_IMPLEMENT_QSORT_EX( icvSortFloat, float, CV_CMP_FLOAT, float)


//===========================================================================
string ToString(int i)
{
    stringstream tmp;
    tmp << i;

    return tmp.str();
}

//===========================================================================
int get_len(const CvMat* mat)
{
    return (mat->cols > mat->rows) ? mat->cols : mat->rows;
}

//===========================================================================
//----------------------------- CvGBTreesParams -----------------------------
//===========================================================================

CvGBTreesParams::CvGBTreesParams() 
            : CvDTreeParams( 3, 10, 0, true, 10, 0, false, false, 0 )
{
    weak_count = 50;
    loss_function_type = CvGBTrees::SQUARED_LOSS;
    subsample_portion = 1.0f;
    shrinkage = 1.0f;
}

//===========================================================================

CvGBTreesParams::CvGBTreesParams( int _loss_function_type, int _weak_count, 
                         float _shrinkage, float _subsample_portion, 
                         int _max_depth, bool _use_surrogates )
            : CvDTreeParams( 3, 10, 0, true, 10, 0, false, false, 0 )
{
    loss_function_type = _loss_function_type;
    weak_count = _weak_count;
    shrinkage = _shrinkage;
    subsample_portion = _subsample_portion;
    max_depth = _max_depth;
    use_surrogates = _use_surrogates;
}

//===========================================================================
//------------------------------- CvGBTrees ---------------------------------
//===========================================================================

CvGBTrees::CvGBTrees()
{
    data = 0;
    weak = 0;
    default_model_name = "my_boost_tree";
    orig_response = sum_response = sum_response_tmp = 0;
    weak_eval = subsample_train = subsample_test = 0;
    missing = sample_idx = 0;
    class_labels = 0;
    class_count = 1;
    delta = 0.0f;
    
    clear();
}

//===========================================================================

void CvGBTrees::clear()
{
    if( weak )
    {
        CvSeqReader reader;
        CvSlice slice = CV_WHOLE_SEQ;
        int weak_count = cvSliceLength( slice, weak[class_count-1] );
        CvDTree* tree;

        //data->shared = false;
        for (int i=0; i<class_count; ++i)
        {
            if ((weak[i]) && (weak_count))
            {
                cvStartReadSeq( weak[i], &reader ); 
                cvSetSeqReaderPos( &reader, slice.start_index );
                for (int j=0; j<weak_count; ++j)
                {
                    CV_READ_SEQ_ELEM( tree, reader );
                    //tree->clear();
                    delete tree;
                    tree = 0;
                }
            }
        }
        for (int i=0; i<class_count; ++i)
            if (weak[i]) cvReleaseMemStorage( &(weak[i]->storage) );
        delete[] weak;
    }
    if (data) 
    {
        data->shared = false;
        delete data;
    }
    weak = 0;
    data = 0;
    delta = 0.0f;
    cvReleaseMat( &orig_response );
    cvReleaseMat( &sum_response );
    cvReleaseMat( &sum_response_tmp );
    cvReleaseMat( &weak_eval );
    cvReleaseMat( &subsample_train );
    cvReleaseMat( &subsample_test );
    cvReleaseMat( &sample_idx );
    cvReleaseMat( &missing );
    cvReleaseMat( &class_labels );
}

//===========================================================================

CvGBTrees::~CvGBTrees()
{
    clear();
}

//===========================================================================

CvGBTrees::CvGBTrees( const CvMat* _train_data, int _tflag,
                  const CvMat* _responses, const CvMat* _var_idx,
                  const CvMat* _sample_idx, const CvMat* _var_type,
                  const CvMat* _missing_mask, CvGBTreesParams _params )
{
    weak = 0;
    data = 0;
    default_model_name = "my_boost_tree";
    orig_response = sum_response = sum_response_tmp = 0;
    weak_eval = subsample_train = subsample_test = 0;
    missing = sample_idx = 0;
    class_labels = 0;
    class_count = 1;
    delta = 0.0f;

    train( _train_data, _tflag, _responses, _var_idx, _sample_idx,
           _var_type, _missing_mask, _params );
}

//===========================================================================

bool CvGBTrees::problem_type() const
{
    switch (params.loss_function_type)
    {
    case DEVIANCE_LOSS: return false;
    default: return true;
    }
}

//===========================================================================

bool 
CvGBTrees::train( CvMLData* data, CvGBTreesParams params, bool update )
{
    bool result;
    result = train ( data->get_values(), CV_ROW_SAMPLE,
            data->get_responses(), data->get_var_idx(),
            data->get_train_sample_idx(), data->get_var_types(),
            data->get_missing(), params, update);
                                         //update is not supported
    return result;
}

//===========================================================================


bool
CvGBTrees::train( const CvMat* _train_data, int _tflag,
              const CvMat* _responses, const CvMat* _var_idx,
              const CvMat* _sample_idx, const CvMat* _var_type,
              const CvMat* _missing_mask,
              CvGBTreesParams _params, bool _update ) //update is not supported
{
    CvMemStorage* storage = 0;

    params = _params;
    bool is_regression = problem_type();

    clear();
    int len = get_len(_responses);

    CvMat* new_responses = cvCreateMat( len, 1, CV_32F);
    cvZero(new_responses);

    data = new CvDTreeTrainData( _train_data, _tflag, new_responses, _var_idx,
        _sample_idx, _var_type, _missing_mask, _params, true, true );
    if (_missing_mask)
    {
        missing = cvCreateMat(_missing_mask->rows, _missing_mask->cols,
                              _missing_mask->type);
        cvCopy( _missing_mask, missing);
    }    

    orig_response = cvCreateMat( _responses->rows, _responses->cols,
                                 _responses->type );
    cvCopy( _responses, orig_response);
    orig_response->step = CV_ELEM_SIZE(_responses->type);

    if (!is_regression)
    {
        int max_label = -1;
        for (int i=0; i<get_len(orig_response); ++i)
            if (max_label < orig_response->data.fl[i])
                max_label = int(orig_response->data.fl[i]);
        max_label++;
        class_labels = cvCreateMat(1, max_label, CV_32S);
        cvZero(class_labels);
        for (int i=0; i<get_len(orig_response); ++i)
            class_labels->data.i[int(orig_response->data.fl[i])] = 1;
        class_count = 0;
        for (int i=0; i<max_label; ++i)
            if (class_labels->data.i[i])
                class_labels->data.i[i] = ++class_count;
    }

    data->is_classifier = false;

    if (_sample_idx)
    {
        sample_idx = cvCreateMat( _sample_idx->rows, _sample_idx->cols,
                                  _sample_idx->type );
        cvCopy( _sample_idx, sample_idx);
        icvSortFloat(sample_idx->data.fl, get_len(sample_idx), 0);
    }
    else
    {
        int n = (_tflag == CV_ROW_SAMPLE) ? _train_data->rows
                                          : _train_data->cols;
        sample_idx = cvCreateMat( 1, n, CV_32S );
        for (int i=0; i<n; ++i)
            sample_idx->data.i[i] = i;
    }

    sum_response = cvCreateMat(class_count, len, CV_32F);
    sum_response_tmp = cvCreateMat(class_count, len, CV_32F);
    cvZero(sum_response);

    delta = 0.0f;
    if (is_regression) base_value = find_optimal_value(sample_idx);
    else base_value = 0.0f;
    cvSet( sum_response, cvScalar(base_value) );

    weak = new pCvSeq[class_count];
    for (int i=0; i<class_count; ++i)
    {
        storage = cvCreateMemStorage();
        weak[i] = cvCreateSeq( 0, sizeof(CvSeq), sizeof(CvDTree*), storage );
        storage = 0;
    }    

    // subsample params and data
    rng = CvRNG(time(0));

    int samples_count = get_len(sample_idx);

    //if ( params.subsample_portion > 1) params.subsample_portion = 1;
    //if ( params.subsample_portion < 0) params.subsample_portion = 1;
    params.subsample_portion = params.subsample_portion <= FLT_EPSILON || 
        1 - params.subsample_portion <= FLT_EPSILON
        ? 1 : params.subsample_portion;
    int train_sample_count = cvFloor(params.subsample_portion * samples_count);
    if (train_sample_count == 0)
        train_sample_count = samples_count;
    int test_sample_count = samples_count - train_sample_count;
    int* idx_data = new int[samples_count];
    subsample_train = cvCreateMatHeader( 1, train_sample_count, CV_32SC1 );
    *subsample_train = cvMat( 1, train_sample_count, CV_32SC1, idx_data );
    if (test_sample_count)
    {
        subsample_test  = cvCreateMatHeader( 1, test_sample_count, CV_32SC1 );
        *subsample_test = cvMat( 1, test_sample_count, CV_32SC1,
                                 idx_data + train_sample_count );
    }


    // training procedure

    for ( int i=0; i < params.weak_count; ++i )
    {
        for ( int m=0; m < class_count; ++m )
        {
            do_subsample();
            find_gradient(m);
            CvDTree* tree = new CvDTree;
            tree->train( data, subsample_train );
            change_values(tree, m);

            if (subsample_test)
            {
                CvMat x;
                CvMat x_miss;
                int* sample_data = sample_idx->data.i;
                int* subsample_data = subsample_test->data.i;
                int s_step = (sample_idx->cols > sample_idx->rows) ? 1
                             : sample_idx->step/CV_ELEM_SIZE(sample_idx->type);
                for (int j=0; j<get_len(subsample_test); ++j)
                {
                    for (int k=0; k<class_count; ++k)
                    {
                        int idx = *(sample_data + subsample_data[j]*s_step);
                        float res = 0.0f;
                        cvGetRow( data->train_data, &x, idx);
                        if (missing)
                        {
                            cvGetRow( missing, &x_miss, idx);
                            res = (float)tree->predict(&x, &x_miss)->value;
                        }
                        else
                        {
                            res = (float)tree->predict(&x)->value;
                        }
                        sum_response_tmp->data.fl[idx + k*len] = 
                                        sum_response->data.fl[idx + k*len] +
                                        params.shrinkage * res;
                    }
                }
            }

            cvSeqPush( weak[m], &tree );
            tree = 0;
        } // m=0..class_count
    CvMat* tmp;
    tmp = sum_response_tmp;
    sum_response_tmp = sum_response;
    sum_response = tmp;
    tmp = 0;
    } // i=0..params.weak_count

    delete[] idx_data;
    cvReleaseMat(&new_responses);
    data->free_train_data();
    return true;

} // CvGBTrees::train(...)

//===========================================================================

float Sign(float x)
  {
  if (x<0.0f) return -1.0f;
  else if (x>0.0f) return 1.0f;
  return 0.0f;
  }

//===========================================================================

void CvGBTrees::find_gradient(const int k)
{
    int* sample_data = sample_idx->data.i;
    int* subsample_data = subsample_train->data.i;
    float* grad_data = data->responses->data.fl;
    float* resp_data = orig_response->data.fl;
    float* current_data = sum_response->data.fl;

    switch (params.loss_function_type)
    // loss_function_type in
    // {SQUARED_LOSS, ABSOLUTE_LOSS, HUBER_LOSS, DEVIANCE_LOSS}
    {
        case SQUARED_LOSS:
        {
            for (int i=0; i<get_len(subsample_train); ++i)
            {
                int s_step = (sample_idx->cols > sample_idx->rows) ? 1
                             : sample_idx->step/CV_ELEM_SIZE(sample_idx->type);
                int idx = *(sample_data + subsample_data[i]*s_step);
                grad_data[idx] = resp_data[idx] - current_data[idx];
            }
        }; break;

        case ABSOLUTE_LOSS:
        {
            for (int i=0; i<get_len(subsample_train); ++i)
            {
                int s_step = (sample_idx->cols > sample_idx->rows) ? 1
                             : sample_idx->step/CV_ELEM_SIZE(sample_idx->type);
                int idx = *(sample_data + subsample_data[i]*s_step);
                grad_data[idx] = Sign(resp_data[idx] - current_data[idx]);
            }
        }; break;

        case HUBER_LOSS:
        {
            float alpha = 0.2f;
            int n = get_len(subsample_train);
            int s_step = (sample_idx->cols > sample_idx->rows) ? 1
                         : sample_idx->step/CV_ELEM_SIZE(sample_idx->type);

            float* residuals = new float[n];
            for (int i=0; i<n; ++i)
            {
                int idx = *(sample_data + subsample_data[i]*s_step);
                residuals[i] = fabs(resp_data[idx] - current_data[idx]);
            }
            icvSortFloat(residuals, n, 0.0f);
            
            delta = residuals[int(ceil(n*alpha))];

            for (int i=0; i<n; ++i)
            {
                int idx = *(sample_data + subsample_data[i]*s_step);
                float r = resp_data[idx] - current_data[idx];
                grad_data[idx] = (fabs(r) > delta) ? delta*Sign(r) : r;
            }
            delete[] residuals;

        }; break;

        case DEVIANCE_LOSS:
        {
            for (int i=0; i<get_len(subsample_train); ++i)
            {
                long double exp_fk = 0;
                long double exp_sfi = 0;
                int s_step = (sample_idx->cols > sample_idx->rows) ? 1
                             : sample_idx->step/CV_ELEM_SIZE(sample_idx->type);
                int idx = *(sample_data + subsample_data[i]*s_step);
            
                for (int j=0; j<class_count; ++j)
                {
                    long double res;
                    res = current_data[idx + j*sum_response->cols];
                    res = expl(res);
                    if (j == k) exp_fk = res;
                    exp_sfi += res;
                }
                int orig_label = int(resp_data[idx]);
                grad_data[idx] = (float)(!(k-class_labels->data.i[orig_label]+1)) -
                                 (float)(exp_fk / exp_sfi);
            }
        }; break;

        default: break;
    }

} // CvGBTrees::find_gradient(...)

//===========================================================================

void CvGBTrees::change_values(CvDTree* tree, const int _k)
{
    CvDTreeNode** predictions = new pCvDTreeNode[get_len(subsample_train)];

    int* sample_data = sample_idx->data.i;
    int* subsample_data = subsample_train->data.i;
    int s_step = (sample_idx->cols > sample_idx->rows) ? 1
                 : sample_idx->step/CV_ELEM_SIZE(sample_idx->type);

    CvMat x;
    CvMat miss_x;

    for (int i=0; i<get_len(subsample_train); ++i)
    {
        int idx = *(sample_data + subsample_data[i]*s_step);
        cvGetRow( data->train_data, &x, idx);
        if (missing)
        {
            cvGetRow( missing, &miss_x, idx);
            predictions[i] = tree->predict(&x, &miss_x);
        }
        else 
            predictions[i] = tree->predict(&x);
    }

    CvDTreeNode** leaves;
    int leaves_count = 0;
    leaves = GetLeaves( tree, leaves_count);

    for (int i=0; i<leaves_count; ++i)
    {
        int samples_in_leaf = 0;
        for (int j=0; j<get_len(subsample_train); ++j)
        {
            if (leaves[i] == predictions[j]) samples_in_leaf++;
        }

        if (!samples_in_leaf) // It should not be done anyways! but...
        {
            leaves[i]->value = 0.0;
            continue; 
        }

        CvMat* leaf_idx = cvCreateMat(1, samples_in_leaf, CV_32S);
        int* leaf_idx_data = leaf_idx->data.i;

        for (int j=0; j<get_len(subsample_train); ++j)
        {
            int idx = *(sample_data + subsample_data[j]*s_step);
            if (leaves[i] == predictions[j])
                *leaf_idx_data++ = idx;
        }

        float value = find_optimal_value(leaf_idx);
        leaves[i]->value = value;

        leaf_idx_data = leaf_idx->data.i;

        int len = sum_response_tmp->cols;
        for (int j=0; j<get_len(leaf_idx); ++j)
        {
            int idx = leaf_idx_data[j];        
            sum_response_tmp->data.fl[idx + _k*len] =
                                    sum_response->data.fl[idx + _k*len] +
                                    params.shrinkage * value;
        }
        leaf_idx_data = 0;     
        cvReleaseMat(&leaf_idx);
    }

    // releasing the memory
    for (int i=0; i<get_len(subsample_train); ++i)
    {
        predictions[i] = 0;
    }
    delete[] predictions;

    for (int i=0; i<leaves_count; ++i)
    {
        leaves[i] = 0;
    }
    delete[] leaves;
}

//===========================================================================
/*
void CvGBTrees::change_values(CvDTree* tree, const int _k)
{
    
    CvDTreeNode** leaves;
    int leaves_count = 0;
    
    leaves = GetLeaves( tree, leaves_count);

    for (int i=0; i<leaves_count; ++i)
    {
        int n = leaves[i]->sample_count;
        int* leaf_idx_data = new int[n];
        data->get_sample_indices(leaves[i], leaf_idx_data);
        CvMat* leaf_idx = 0;
        cvInitMatHeader(leaf_idx, n, 1, CV_32S, leaf_idx_data);

        float value = find_optimal_value(leaf_idx);
        leaves[i]->value = value;

        int len = sum_response_tmp->cols;
        for (int j=0; j<n; ++j)
        {
            int idx = leaf_idx_data[j] + _k*len;
            sum_response_tmp->data.fl[idx] = sum_response->data.fl[idx] +
                                             params.shrinkage * value;
        }
        leaf_idx_data = 0;
        cvReleaseMat(&leaf_idx);
    }

    // releasing the memory
    for (int i=0; i<leaves_count; ++i)
    {
        leaves[i] = 0;
    }
    delete[] leaves;
}    //change_values(...);
*/
//===========================================================================

float CvGBTrees::find_optimal_value( const CvMat* _Idx )
{

    long double gamma = (long double)0.0;

    int* idx = _Idx->data.i;
    float* resp_data = orig_response->data.fl;
    float* cur_data = sum_response->data.fl;
    int n = get_len(_Idx);

    switch (params.loss_function_type)
    // SQUARED_LOSS=0, ABSOLUTE_LOSS=1, HUBER_LOSS=3, DEVIANCE_LOSS=4
    {
    case SQUARED_LOSS:
        {
            for (int i=0; i<n; ++i)
                gamma += resp_data[idx[i]] - cur_data[idx[i]];
            gamma /= (long double)n;
        }; break;

    case ABSOLUTE_LOSS:
        {
            float* residuals = new float[n];
            for (int i=0; i<n; ++i)
                residuals[i] = (resp_data[*idx] - cur_data[*idx++]);
            icvSortFloat(residuals, n, 0.0f);
            if (n % 2) 
                gamma = residuals[n/2];
            else gamma = (residuals[n/2-1] + residuals[n/2]) / 2.0f;
            delete[] residuals;
        }; break;

    case HUBER_LOSS:
        {
            float* residuals = new float[n];
            for (int i=0; i<n; ++i)
                residuals[i] = (resp_data[*idx] - cur_data[*idx++]);
            icvSortFloat(residuals, n, 0.0f);

            int n_half = n >> 1;
            float r_median = (n == n_half<<1) ?
                        (residuals[n_half-1] + residuals[n_half]) / 2.0f :
                        residuals[n_half];

            for (int i=0; i<n; ++i)
            {
                float dif = residuals[i] - r_median;
                gamma += (delta < fabs(dif)) ? Sign(dif)*delta : dif;
            }
            gamma /= (long double)n;
            gamma += r_median;
            delete[] residuals;

        }; break;

    case DEVIANCE_LOSS:
        {
            float* grad_data = data->responses->data.fl;
            long double tmp1 = 0;
            long double tmp2 = 0;
            long double tmp  = 0;
            for (int i=0; i<n; ++i)
            {
                tmp = grad_data[idx[i]];
                tmp1 += tmp;
                tmp2 += fabs(tmp)*(1-fabs(tmp));
            };
            if (tmp2 == 0) 
            {
                tmp2 = 1;
            }

            gamma = ((long double)(class_count-1)) / (long double)class_count * (tmp1/tmp2);
        }; break;

    default: break;
    }

    return float(gamma);

} // CvGBTrees::find_optimal_value

//===========================================================================


void CvGBTrees::leaves_get( CvDTreeNode** leaves, int& count, CvDTreeNode* node )
{
    if (node->left != NULL)  leaves_get(leaves, count, node->left);
    if (node->right != NULL) leaves_get(leaves, count, node->right);
    if ((node->left == NULL) && (node->right == NULL))
        leaves[count++] = node;
}

//---------------------------------------------------------------------------

CvDTreeNode** CvGBTrees::GetLeaves( const CvDTree* dtree, int& len )
{
    len = 0;
    CvDTreeNode** leaves = new pCvDTreeNode[1 << params.max_depth];
    leaves_get(leaves, len, const_cast<pCvDTreeNode>(dtree->get_root()));
    return leaves;
}

//===========================================================================

void CvGBTrees::do_subsample()
{

    int n = get_len(sample_idx);
    int* idx = subsample_train->data.i;

    for (int i = 0; i < n; i++ )
        idx[i] = i;

    if (subsample_test)
        for (int i = 0; i < n; i++)
        {
            int a = cvRandInt( &rng ) % n;
            int b = cvRandInt( &rng ) % n;
            int t;
            CV_SWAP( idx[a], idx[b], t );
        }

/*
    int n = get_len(sample_idx);
    if (subsample_train == 0)
        subsample_train = cvCreateMat(1, n, CV_32S);
    int* subsample_data = subsample_train->data.i;
    for (int i=0; i<n; ++i)
        subsample_data[i] = i;
    subsample_test = 0;
*/
}

//===========================================================================

float CvGBTrees::predict( const CvMat* _sample, const CvMat* _missing,
        CvMat* weak_responses, CvSlice slice, int k) const 
{
    float result = 0.0f;

    if (!weak) return 0.0f;

    float* sum = new float[class_count];
    for (int i=0; i<class_count; ++i)
        sum[i] = base_value;

    CvSeqReader reader;
    int weak_count = cvSliceLength( slice, weak[class_count-1] );
    CvDTree* tree;

    for (int i=0; i<class_count; ++i)
    {
        if ((weak[i]) && (weak_count))
        {
            cvStartReadSeq( weak[i], &reader ); 
            cvSetSeqReaderPos( &reader, slice.start_index );
            for (int j=0; j<weak_count; ++j)
            {
                CV_READ_SEQ_ELEM( tree, reader );
                sum[i] += params.shrinkage *
                         (float)(tree->predict(_sample, _missing)->value);
            }
        }
    }

    if (class_count == 1)
    {
        result = sum[0];
        delete[] sum;
        return result;
    }

    if ((k>=0) && (k<class_count))
    {
        result = sum[k];
        delete[] sum;
        return result;
    }

    float max = sum[0];
    int class_label = 0;
    for (int i=1; i<class_count; ++i)
        if (sum[i] > max)
        {
            max = sum[i];
            class_label = i;
        }

    delete[] sum;

    int orig_class_label = -1;
    for (int i=0; i<get_len(class_labels); ++i)
        if (class_labels->data.i[i] == class_label+1)
            orig_class_label = i;

    return float(orig_class_label);
}

//===========================================================================

void CvGBTrees::write_params( CvFileStorage* fs ) const
{
    CV_FUNCNAME( "CvGBTrees::write_params" );
    __BEGIN__;
    
    const char* loss_function_type_str =
        params.loss_function_type == SQUARED_LOSS ? "SquaredLoss" :
        params.loss_function_type == ABSOLUTE_LOSS ? "AbsoluteLoss" :
        params.loss_function_type == HUBER_LOSS ? "HuberLoss" :
        params.loss_function_type == DEVIANCE_LOSS ? "DevianceLoss" : 0;


    if( loss_function_type_str )
        cvWriteString( fs, "loss_function", loss_function_type_str );
    else
        cvWriteInt( fs, "loss_function", params.loss_function_type );

    cvWriteInt( fs, "ensemble_length", params.weak_count );
    cvWriteReal( fs, "shrinkage", params.shrinkage );
    cvWriteReal( fs, "subsample_portion", params.subsample_portion );
    //cvWriteInt( fs, "max_tree_depth", params.max_depth );
    //cvWriteString( fs, "use_surrogate_splits", params.use_surrogates ? "true" : "false");
    if (class_labels) cvWrite( fs, "class_labels", class_labels);

    data->is_classifier = !problem_type();
    data->write_params( fs );
    data->is_classifier = 0;

    __END__;
}


//===========================================================================

void CvGBTrees::read_params( CvFileStorage* fs, CvFileNode* fnode )
{
    CV_FUNCNAME( "CvGBTrees::read_params" );
    __BEGIN__;


    CvFileNode* temp;

    if( !fnode || !CV_NODE_IS_MAP(fnode->tag) )
        return;

    data = new CvDTreeTrainData();
    CV_CALL( data->read_params(fs, fnode));
    data->shared = true;

    params.max_depth = data->params.max_depth;
    params.min_sample_count = data->params.min_sample_count;
    params.max_categories = data->params.max_categories;
    params.priors = data->params.priors;
    params.regression_accuracy = data->params.regression_accuracy;
    params.use_surrogates = data->params.use_surrogates;

    temp = cvGetFileNodeByName( fs, fnode, "loss_function" );
    if( !temp )
        EXIT;

    if( temp && CV_NODE_IS_STRING(temp->tag) )
    {
        const char* loss_function_type_str = cvReadString( temp, "" );
        params.loss_function_type = strcmp( loss_function_type_str, "SquaredLoss" ) == 0 ? SQUARED_LOSS :
                            strcmp( loss_function_type_str, "AbsoluteLoss" ) == 0 ? ABSOLUTE_LOSS :
                            strcmp( loss_function_type_str, "HuberLoss" ) == 0 ? HUBER_LOSS :
                            strcmp( loss_function_type_str, "DevianceLoss" ) == 0 ? DEVIANCE_LOSS : -1;
    }
    else
        params.loss_function_type = cvReadInt( temp, -1 );


    if( params.loss_function_type < SQUARED_LOSS || params.loss_function_type > DEVIANCE_LOSS ||  params.loss_function_type == 2)
        CV_ERROR( CV_StsBadArg, "Unknown loss function" );

    params.weak_count = cvReadIntByName( fs, fnode, "ensemble_length" );
    params.shrinkage = (float)cvReadRealByName( fs, fnode, "shrinkage", 0.1 );
    params.subsample_portion = (float)cvReadRealByName( fs, fnode, "subsample_portion", 1.0 );

    if (data->is_classifier)
    {
        class_labels = (CvMat*)cvReadByName( fs, fnode, "class_labels" );
        if( class_labels && !CV_IS_MAT(class_labels))
            CV_ERROR( CV_StsParseError, "class_labels must stored as a matrix");
    }
    data->is_classifier = 0;

    __END__;
}




void CvGBTrees::write( CvFileStorage* fs, const char* name ) const
{
    CV_FUNCNAME( "CvGBTrees::write" );

    __BEGIN__;

    CvSeqReader reader;
    int i;
    std::string s;

    cvStartWriteStruct( fs, name, CV_NODE_MAP, CV_TYPE_NAME_ML_GBT );

    if( !weak )
        CV_ERROR( CV_StsBadArg, "The model has not been trained yet" );

    write_params( fs );
    cvWriteReal( fs, "base_value", base_value);
    cvWriteInt( fs, "class_count", class_count);

    for ( int j=0; j < class_count; ++j )
    {
        s = "trees_";
        s += ToString(j);
        cvStartWriteStruct( fs, s.c_str(), CV_NODE_SEQ );

        cvStartReadSeq( weak[j], &reader );

        for( i = 0; i < weak[j]->total; i++ )
        {
            CvDTree* tree;
            CV_READ_SEQ_ELEM( tree, reader );
            cvStartWriteStruct( fs, 0, CV_NODE_MAP );
            tree->write( fs );
            cvEndWriteStruct( fs );
        }

        cvEndWriteStruct( fs );
    }

    cvEndWriteStruct( fs );

    __END__;
}


//===========================================================================


void CvGBTrees::read( CvFileStorage* fs, CvFileNode* node )
{
  
    CV_FUNCNAME( "CvGBTrees::read" );

    __BEGIN__;

    CvSeqReader reader;
    CvFileNode* trees_fnode;
    CvMemStorage* storage;
    int i, ntrees;
    std::string s;

    clear();
    read_params( fs, node );

    if( !data )
        EXIT;

    base_value = (float)cvReadRealByName( fs, node, "base_value", 0.0 );
    class_count = cvReadIntByName( fs, node, "class_count", 1 );

    weak = new pCvSeq[class_count];


    for (int j=0; j<class_count; ++j)
    { 
        s = "trees_";
        s += ToString(j);

        trees_fnode = cvGetFileNodeByName( fs, node, s.c_str() );
        if( !trees_fnode || !CV_NODE_IS_SEQ(trees_fnode->tag) )
            CV_ERROR( CV_StsParseError, "<trees_x> tag is missing" );

        cvStartReadSeq( trees_fnode->data.seq, &reader );
        ntrees = trees_fnode->data.seq->total;

        if( ntrees != params.weak_count )
            CV_ERROR( CV_StsUnmatchedSizes,
            "The number of trees stored does not match <ntrees> tag value" );

        CV_CALL( storage = cvCreateMemStorage() );
        weak[j] = cvCreateSeq( 0, sizeof(CvSeq), sizeof(CvDTree*), storage );

        for( i = 0; i < ntrees; i++ )
        {
            CvDTree* tree = new CvDTree();
            CV_CALL(tree->read( fs, (CvFileNode*)reader.ptr, data ));
            CV_NEXT_SEQ_ELEM( reader.seq->elem_size, reader );
            cvSeqPush( weak[j], &tree );
        }
    }

    __END__;
}

//===========================================================================

// type in {CV_TRAIN_ERROR, CV_TEST_ERROR}
float 
CvGBTrees::calc_error( CvMLData* _data, int type, std::vector<float> *resp )
{
    float err = 0;
    const CvMat* values = _data->get_values();
    const CvMat* response = _data->get_responses();
    const CvMat* missing = _data->get_missing();
    const CvMat* sample_idx = (type == CV_TEST_ERROR) ?
                              _data->get_test_sample_idx() :
                              _data->get_train_sample_idx();
    //const CvMat* var_types = _data->get_var_types();
    int* sidx = sample_idx ? sample_idx->data.i : 0;
    int r_step = CV_IS_MAT_CONT(response->type) ?
                1 : response->step / CV_ELEM_SIZE(response->type);
    //bool is_classifier = 
    //            var_types->data.ptr[var_types->cols-1] == CV_VAR_CATEGORICAL;
    int sample_count = sample_idx ? sample_idx->cols : 0;
    sample_count = (type == CV_TRAIN_ERROR && sample_count == 0) ?
                                        values->rows :
                                        sample_count;
    float* pred_resp = 0;
    if( resp && (sample_count > 0) )
    {
        resp->resize( sample_count );
        pred_resp = &((*resp)[0]);
    }
    if ( !problem_type() )
    {
        for( int i = 0; i < sample_count; i++ )
        {
            CvMat sample, miss;
            int si = sidx ? sidx[i] : i;
            cvGetRow( values, &sample, si ); 
            if( missing ) 
                cvGetRow( missing, &miss, si );             
            float r = (float)predict( &sample, missing ? &miss : 0 );
            if( pred_resp )
                pred_resp[i] = r;
            int d = fabs((double)r - response->data.fl[si*r_step]) <= FLT_EPSILON ? 0 : 1;
            err += d;
        }
        err = sample_count ? err / (float)sample_count * 100 : -FLT_MAX;
    }
    else
    {
        for( int i = 0; i < sample_count; i++ )
        {
            CvMat sample, miss;
            int si = sidx ? sidx[i] : i;
            cvGetRow( values, &sample, si );
            if( missing ) 
                cvGetRow( missing, &miss, si );             
            float r = (float)predict( &sample, missing ? &miss : 0 );
            if( pred_resp )
                pred_resp[i] = r;
            float d = r - response->data.fl[si*r_step];
            err += d*d;
        }
        err = sample_count ? err / (float)sample_count : -FLT_MAX;    
    }
    return err;

}