backpropagation
==============================

.. js:function:: MaxPoolingLayer.backpropagation() 

    誤差逆伝播

ソース
^^^^^^

.. code-block:: js

            backpropagation() {
                var lap = new Lap(this.backwardTime);
    
                var prev_layer = this.prevLayer;
    
                Assert(this.y_.dt.length == this.nextLayer.deltaX.dt.length);
    
                for(var i = 0; i < this.deltaX.dt.length; i++){
                    this.deltaX.dt[i] = 0;
                }
                lap.Time();
    
                // 出力先
                var output_idx = 0;
    
                // バッチ内のデータに対し
                for (var batch_idx = 0; batch_idx < miniBatchSize; batch_idx++) {
    
                    // すべての特徴マップに対し
                    for (var channel_idx = 0; channel_idx < this.numChannels; channel_idx++) {
                        var offset = batch_idx * prev_layer.unitSize + channel_idx * prev_layer.numRows * prev_layer.numCols;
    
                        // 出力の行に対し
                        for (var r1 = 0; r1 < this.numRows; r1++) {
                            var r0 = r1 * this.filterSize;
    
                            // 出力の列に対し
                            for (var c1 = 0; c1 < this.numCols; c1++) {
                                var c0 = c1 * this.filterSize;
    
                                var delta = this.nextLayer.deltaX.dt[output_idx];
                                if(delta != 0){
    
                                    var r2 = this.maxRow[output_idx] | 0;
                                    var c2 = this.maxCol[output_idx] | 0;
                                    var prev_y_idx = offset + (r0 + r2) * prev_layer.numCols + (c0 + c2);
                                    this.deltaX.dt[prev_y_idx] += delta;
                                }
    
                                output_idx++;
                            }
                        }
                    }
                }
    
                Assert(output_idx == this.nextLayer.deltaX.dt.length);
                lap.Time();
            }