dnn_layer_drop.h

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// Copyright 2019 Claes Rolen (www.rolensystems.com)
//
//   Licensed under the Apache License, Version 2.0 (the "License");
//   you may not use this file except in compliance with the License.
//   You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
//   Unless required by applicable law or agreed to in writing, software
//   distributed under the License is distributed on an "AS IS" BASIS,
//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//   See the License for the specific language governing permissions and
//   limitations under the License.

#pragma once
namespace dnn
{

class layer_drop: public layer
{
private:
    arma::Mat<DNN_Dtype> drop_mask;     
    DNN_Dtype p;                        
public:
    layer_drop(DNN_Dtype prob):layer()
    {
        p     = prob;
        type  = "Dropout";
        char s[100];
        std::snprintf(s,100,"(%g)",p);
        id    = type+std::string(s);
    };

    virtual void init(void)
    {
        layer::init();
         // Default to same as previous layer
        N_cols_right     = N_cols_left;
        N_rows_right     = N_rows_left;
        N_channels_right = N_channels_left;
        N_right          = N_left;
        train_par        = true;
    }

    void upd_buf_size(arma::uword nmb)
    {
        layer::upd_buf_size(nmb);
        drop_mask.set_size(N_right, N_batch); drop_mask.zeros();
    }

    void prop_mb(void)
    {
        if(phase == PHASE::TRAIN )
        {
            const arma::uword N_ = N_left*N_batch;
            arma::Col<DNN_Dtype> p_mat(N_,arma::fill::randu);
            drop_mask.zeros();
            drop_mask.elem(arma::find(p_mat < p)).fill(1/p); // Inverted dropout
            Y = *(left->get_Y_ptr())%drop_mask;
        }
        else
        {
            Y = *(left->get_Y_ptr());
        }
    }

    void backprop(void)
    {
        Dleft = *(right->get_Dleft_ptr())%drop_mask;      // Back prop
    }

    void disp(void)
    {
        layer::disp();
        std::cout << "Dropout rate:         " << p << std::endl;
    }
}; // End class layer_drop
} // End namespace dnn