\begin{tikzpicture}[scale=0.50]
	\begin{axis}[
			xmin=-2.5, xmax=2.5,
			ymin=-0.1, ymax=1.1,
			axis lines=center,
			axis on top=true,
			%domain=-2.5:2.5,
			ylabel=$y$,
			xlabel=$\sum_{i=1}^{4} w_{i}x_{i}$,
		]
		
		\addplot [smooth,mark=none,draw=blue,] {1/(1+exp(-2.5*\x)};
		%% Add the asymptotes
		\draw [blue, dotted, thick] (axis cs:4,+1)-- (axis cs:0,+1);
	\end{axis}
\end{tikzpicture}