April 2020
Intermediate to advanced
552 pages
6h 13m
Japanese
Content preview from ゼロから作るDeep Learning ❸ ―フレームワーク編
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ステップ39和を求める関数
本ステップでは、DeZeroの和を求める関数――sum関数――を実装します。まずは「足し算」の微分について復習し、それを応用してsum関数の微分を導きます。その後で、sum関数を実装するという流れで進めていきます。
39.1 sum関数の逆伝播
私たちは「足し算」を行う関数はすでに実装済みです。足し算の微分は、
のとき、
、
となります。そのため逆伝播では、出力側から伝わる勾配を、そのまま入力側に流すだけでした。これは図で示せば、図39-1のようになります。
図39-1 足し算の順伝播と逆伝播
図39-1の計算では、足し算を行った後に、変数yから逆伝播を行います。このとき、変数x0とx1には、出力側から伝わる1という勾配を2つに「コピー」して流します。これが足し算の逆伝播です。この足し算の逆伝播は、2つの要素を持つベクトルでも同じように成り立ちます。それでは、 ...
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