figure-four-layers-of-neural-network.tex

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\begin{tikzpicture}
\begin{scope}[]

\def\neuronsep{1.5}

\tikzstyle{neuronnode} = [minimum size=2em,circle,draw,ublue,very thick,inner sep=1pt, fill=white,align=center,drop shadow={shadow xshift=0.1em,shadow yshift=-0.1em}]

%%% layer 1
\foreach \n in {1,...,5}{
    \node [neuronnode] (neuron0\n) at (\n * \neuronsep,0) {\tiny{$f_1$}\\[-1ex] \tiny{$\sum$}};
    \draw [-,ublue] (neuron0\n.east) -- (neuron0\n.west);
}

\foreach \n in {1,...,5}{
    \foreach \m in {1,...,5}{
        \draw [<-] ([yshift=-0.1em]neuron0\m.south) -- ([yshift=-1.8em]neuron0\n.south);
    }
    \node [anchor=north] (x\n) at ([yshift=-2em]neuron0\n.south) {$x_\n$};
}

\node [anchor=west] (w1label) at ([xshift=-0.5em,yshift=0.8em]x5.north east) {${\mathbi{W}}^{[1]}$};

\begin{pgfonlayer}{background}
\node [rectangle,inner sep=0.2em,fill=red!20] [fit = (neuron01) (neuron05)] (layer01) {};
\end{pgfonlayer}

\node [anchor=west] (layer00label) at ([xshift=1.4em]x5.east) {\footnotesize{第0层}};
\node [anchor=west] (layer00label2) at (layer00label.east) {\footnotesize{（输入层）}};
{
\node [anchor=west] (layer01label) at ([xshift=1em]layer01.east) {\footnotesize{第1层}};
}
{
\node [anchor=west] (layer01label2) at (layer01label.east) {\footnotesize{（{隐层}）}};
}

%%% layer 2
{
\foreach \n in {2,...,4}{
    \node [neuronnode] (neuron1\n) at (\n * \neuronsep,4.5em) {\tiny{$f_2$}\\[-1ex] \tiny{$\sum$}};
    \draw [-,ublue] (neuron1\n.east) -- (neuron1\n.west);
}

\foreach \n in {2,...,4}{
    \foreach \m in {1,...,5}{
        \draw [<-] ([yshift=-0.1em]neuron1\n.south) -- (neuron0\m.north);
    }
}

\node [anchor=west] (w2label) at ([xshift=-2.5em,yshift=5.4em]x5.north east) {${\mathbi{W}}^{[2]}$};

\begin{pgfonlayer}{background}
{
\node [rectangle,inner sep=0.2em,fill=ugreen!20] [fit = (neuron12) (neuron14)] (layer02) {};
}
\end{pgfonlayer}

\node [anchor=west] (layer02label) at ([xshift=5em]layer02.east) {\footnotesize{第2层}};
{
\node [anchor=west] (layer02label2) at (layer02label.east) {\footnotesize{（{隐层}）}};
}
}

%%% layer 3
{
\foreach \n in {1,...,5}{
    \node [neuronnode] (neuron2\n) at (\n * \neuronsep,9em) {\tiny{$f_3$}\\[-1ex] \tiny{$\sum$}};
    \draw [-,ublue] (neuron2\n.east) -- (neuron2\n.west);
}

\foreach \n in {1,...,5}{
    \foreach \m in {2,...,4}{
        \draw [<-] ([yshift=-0.1em]neuron2\n.south) -- (neuron1\m.north);
    }

    \node [anchor=south] (y\n) at ([yshift=1.2em]neuron2\n.north) {$y_\n$};
    \draw [<-,thick] ([yshift=1.1em]neuron2\n.north) -- (neuron2\n.north);
}

\node [anchor=west] (w3label) at ([xshift=-2.5em,yshift=9.5em]x5.north east) {${\mathbi{W}}^{[3]}$};

\begin{pgfonlayer}{background}
{
\node [rectangle,inner sep=0.2em,fill=blue!20] [fit = (neuron21) (neuron25)] (layer03) {};
}
\end{pgfonlayer}

\node [anchor=west] (layer03label) at ([xshift=1em]layer03.east) {\footnotesize{第3层}};
{
\node [anchor=west] (layer03label2) at (layer03label.east) {\footnotesize{（{输出层}）}};
}
}

\end{scope}
\end{tikzpicture}
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