Label Tikz Paths

Question

I am trying to create a simple neural network structure and have the following:

\def\layersep{2.5cm}
\begin{tikzpicture}[shorten >=1pt,->,draw=black!50, node distance=\layersep]
    \tikzstyle{every pin edge}=[<-,shorten <=1pt]
    \tikzstyle{neuron}=[circle,draw=black!80,thick,minimum size=17pt,inner
        sep=0pt]
    \tikzstyle{annot} = [text width=4em, text centered]

    \foreach \name / \y in {1,...,3}
        \path[yshift=0.5cm]
            node[neuron] (H-\name) at (\layersep,-\y cm) {$x_\y$};

    \node[neuron,pin={[pin edge={->}]right:$h_\theta(x)$}, right of=H-2] (O) {};

    \foreach \source in {1,...,3}
        \path (H-\source) edge (O);

\end{tikzpicture}

Which, when rendered, produces the following:

I want to be able to label the \path, but everywhere I've looked talks only about labeling a \draw or \node. I thought I should be able to add:

\path (H-\source) edge (O) {Label Text};

Or set the label attribute in the edge:

\path (H-\source) edge[label=Label Text] (O);

But it doesn't seem to work.

I realize the this segment:

\foreach \source in {1,...,3}
    \path (H-\source) edge (O);

sets the edges. I've also tried creating a new node inside the loop, but wasn't sure what how to position it relative to the edge, because the edge does not have an identifier.

Thanks so much for your help!

Answer 1

Look up the syntax of the basic tikz commands in some tutorial. To add labels, you need a node. E.g., you can have arrows with labels by using

\draw[->] (H-\source) -- node[above]{a\source} (O);

or

\path (H-\source) edge node[above]{a\source} (O);

\documentclass[border=2mm]{standalone}
\usepackage{tikz}
\begin{document}
\def\layersep{2.5cm}
\begin{tikzpicture}%
  [shorten >=1pt,->,draw=black!50, node distance=\layersep,
   every pin edge/.style={<-,shorten <=1pt},
   neuron/.style={circle,draw=black!80,thick,minimum size=17pt,inner
        sep=0pt},
   annot/.style = {text width=4em, text centered}
  ]
  \foreach \name / \y in {1,...,3}
     \node[neuron,yshift=0.5cm] (H-\name) at (\layersep,-\y cm) {$x_\y$};
  \node[neuron,pin={[pin edge={->}]right:$h_\theta(x)$}, right of=H-2] (O) {};
  \foreach \source in {1,...,3}
     \draw[->] (H-\source) -- node[above]{a\source} (O);
\end{tikzpicture}
\end{document}

Answer 2

Let me convert my comments to answer:

for example \path (H-\source) edge ["Label Text"] (O); (needed quotes library) or \path (H-\source) edge node[above] {Label Text} (O); ... is this what you looking for?

Consider the first possibilities, library chains and positioning for neurons positioning and correct syntax for this, your MWE becomes:

\documentclass[tikz, border=2mm]{standalone}
\usetikzlibrary{chains, positioning, quotes}

\begin{document}
\def\layersep{12mm}
\begin{tikzpicture}[shorten >=1pt, ->, draw=black!50, 
           node distance = \layersep and 2*\layersep,
             start chain = going below,
   every pin edge/.style = {<-,shorten <=1pt},
           neuron/.style = {circle,draw=black!80, thick,
                            minimum size=17pt, inner sep=0pt,
                            on chain},
            annot/.style = {text width=4em, text centered},
every edge quotes/.style = {above,font=\footnotesize}
                    ]
\foreach \y in {1,2,3}
     \node (H-\y) [neuron] {$x_\y$};
\node (O) [neuron,pin={[pin edge={->}]right:$h_\theta(x)$}, 
      right=of H-2] {};
\foreach \y in {1,2,3}
     \draw[->] (H-\y) edge [above,"a\y"] (O);
\end{tikzpicture}
\end{document}

I'm pretty sure, that few days ago I wrote answer on very similar question.