[Tex/LaTex] Arrow indicating cycle between two pictures using TikZ — missing arrowheads

arrowstikz-pgf

I'm trying to draw two arrows that should indicate that a neural network cycles between two states. Following the tutorial for the Petri net, I used pgfonlayer, fit and a scope to align two networks side by side. I cannot, however, get the arrow to appear, for some reason. Here is the code

\begin{tikzpicture}[auto]
\node[excited] (middle)                  {-2.5};
\node[inhibited]   (west)  [left=of middle]   {0.5}
    edge node {-1} (middle);
\node[inhibited]   (east)  [right=of middle]  {0.5}
    edge node {-1} (middle);
\node[excited] (north) [above=of middle]  {0.5}
    edge node       {1}  (east)
    edge node[swap] {1}  (west)
    edge node       {-1} (middle);
\node[excited]   (south) [below=of middle]  {0.5}
    edge node        {-1} (middle)
    edge node        {1}  (west)
    edge node [swap] {1}  (east);
\begin{scope}[xshift=6cm]
\node[excited] (middle1)                  {-2.5};
\node[excited]   (west1)  [left=of middle1]   {0.5}
    edge node {-1} (middle1);
\node[excited]   (east1)  [right=of middle1]  {0.5}
    edge node {-1} (middle1);
\node[inhibited] (north1) [above=of middle1]  {0.5}
    edge node       {1}  (east1)
    edge node[swap] {1}  (west1)
    edge node       {-1} (middle1);
\node[inhibited]   (south1) [below=of middle1]  {0.5}
    edge node        {-1} (middle1)
    edge node        {1}  (west1)
    edge node [swap] {1}  (east1);
\end{scope}
\begin{pgfonlayer}{background}
    \node (n1) [fit=(west) (middle) (east) (south) (north)] {};
    \node (n2) [fit=(west1) (middle1) (east1) (south1) (north1)] {};
    \draw [shorten >=5mm,shorten <=5mm,bend left=45,<-]
        (north) to (north1);
    \draw [shorten >=5mm,shorten <=5mm,bend right=45,->]
        (south) to (south1);
\end{pgfonlayer}
\end{tikzpicture}

And the result, regardless of me having <- and -> in the \draw command.
result

Does anyone have an idea why this is happening?

Thanks for the help.

Best Answer

Would this be what you seek? You code is incompleted where this solution added some in order to get the output you posted.

enter image description here

Code

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,intersections,calc,fit}

\tikzset{
 excited/.style={circle,thick,draw=black,fill=blue!50,minimum size=6mm},
 inhibited/.style={circle,thick,draw,fill=none,minimum size=6mm},
 every fit/.append style=text badly centered   % to get rid of underfull bad box
 }

\begin{document}

\pgfdeclarelayer{background}
\pgfdeclarelayer{foreground}
\pgfsetlayers{background,main,foreground}

\begin{tikzpicture}[auto]
\node[excited] (middle)                  {-2.5};
\node[inhibited]   (west)  [left=of middle]   {0.5}
    edge node {-1} (middle);
\node[inhibited]   (east)  [right=of middle]  {0.5}
    edge node {-1} (middle);
\node[excited] (north) [above=of middle]  {0.5}
    edge node       {1}  (east)
    edge node[swap] {1}  (west)
    edge node       {-1} (middle);
\node[excited]   (south) [below=of middle]  {0.5}
    edge node        {-1} (middle)
    edge node        {1}  (west)
    edge node [swap] {1}  (east);
\begin{scope}[xshift=6cm]
\node[excited] (middle1)                  {-2.5};
\node[excited]   (west1)  [left=of middle1]   {0.5}
    edge node {-1} (middle1);
\node[excited]   (east1)  [right=of middle1]  {0.5}
    edge node {-1} (middle1);
\node[inhibited] (north1) [above=of middle1]  {0.5}
    edge node       {1}  (east1)
    edge node[swap] {1}  (west1)
    edge node       {-1} (middle1);
\node[inhibited]   (south1) [below=of middle1]  {0.5}
    edge node        {-1} (middle1)
    edge node        {1}  (west1)
    edge node [swap] {1}  (east1);
\end{scope}
\begin{pgfonlayer}{background}
    \node (n1) [fit=(west) (middle) (east) (south) (north)] {};
    \node (n2) [fit=(west1) (middle1) (east1) (south1) (north1)] {};
    \draw [shorten >=5mm,shorten <=5mm,bend left=45,<-]
        (north) to (north1);
    \draw [shorten >=5mm,shorten <=5mm,bend right=45,->]
        (south) to (south1);
\end{pgfonlayer}
\end{tikzpicture}

\end{document}
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