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\begin{tikzpicture}
\begin{scope}
\node [anchor=center,minimum height=1.7em,fill=yellow!30,draw] (h) at (0,0) {${\mathbi{h}}^{K-1}$};
\node [anchor=west,minimum height=1.7em,fill=blue!30,draw] (s) at ([xshift=6.0em]h.east) {${\mathbi{s}}^{K}$};

\draw [->] (h.east) -- (s.west);


\node [anchor=south west,inner sep=2pt] (step100) at ([xshift=0.5em,yshift=-0.8em]h.north east) {\scriptsize{${\mathbi{s}}^K = {\mathbi{h}}^{K-1} {\mathbi{W}}^K$}};


\node [anchor=south west] (slabel) at ([yshift=1em,xshift=0.3em]s.north) {\scriptsize{\textbf{{已经得到：${\bm \pi}^K = \frac{\partial L}{\partial {\mathbi{s}}^K}$}}}};
\draw [->] ([yshift=0.3em]slabel.south) .. controls +(south:0.5) and +(north:0.5) .. ([xshift=0.5em,yshift=0.1em]s.north);

{
\draw [->,very thick,red] ([yshift=1em,xshift=-0.1em]s.north) -- ([yshift=1.0em,xshift=0.1em]h.north) node [pos=0.5,above] {\scriptsize{{$\frac{\partial L}{\partial {\mathbi{W}}^K} = ?$, $\frac{\partial L}{\partial {\mathbi{h}}^{K-1}} = ?$}}};
\draw [-,very thick,red] ([yshift=0.5em]h.north) -- ([yshift=1.5em]h.north);
\draw [-,very thick,red] ([yshift=0.5em]s.north) -- ([yshift=1.5em]s.north);
}

\end{scope}

\end{tikzpicture}

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