How to draw sigmoid function in flowchart block in latex

Question

How can I draw the gausian functions sign inside the flowchart block (those circles)?

The code I have is:

\usepackage{tikz}
\usetikzlibrary{arrows.meta,calc,chains,shapes.geometric,backgrounds,fit,arrows,positioning}
\tikzset{
  blockk/.style={
  draw,
  fill=blue!20,
  rectangle,
  minimum height=2.5em,
  minimum width=2.5em
  },
sum/.style={
  draw,
  fill=blue!20,
  circle,
  minimum size=0.5cm,
  },
  neu/.style={
  draw,
  fill=blue!20,
  circle,
  minimum size=0.5cm,
  },
input/.style={coordinate},
output/.style={coordinate},
pinstyle/.style={
  pin edge={to-,thin,black}
  }
}
\begin{figure}
\begin{adjustbox}{width=\textwidth,height=\textheight,keepaspectratio}
\begin{tikzpicture}[auto,>=latex']
    % We start by placing the blocks
    \node [input, name=input1] {};
    %fuzzification
    \node [neu, above = of input1] (neu) {};
    \node [neu, right = of neu] (neu1) {};
    \node [neu, right = of neu1] (neu2) {};
    \node [neu, right = of neu2] (neu3) {};
    %memberships
    \node [neu, above left = 0.5 and 0 of neu] (membership1) {};
    \node [neu, above right = 0.5 and 0 of neu] (membership2) {};
    \node [neu, above left = 0.5 and 0 of neu1] (membership3) {};
    \node [neu, above right = 0.5 and 0 of neu1] (membership4) {};
    \node [neu, above left = 0.5 and 0 of neu2] (membership5) {};
    \node [neu, above right = 0.5 and 0 of neu2] (membership6) {};
    \node [neu, above left = 0.5 and 0 of neu3] (membership7) {};
    \node [neu, above right = 0.5 and 0 of neu3] (membership8) {};
    %Rules firing
    \node [neu, above  = 2.5 of neu] (rule1) {$\bar{z}l$};
    \node [neu, right = of rule1] (rule2) {$\bar{z}_r$};
    \node [neu, right = of rule2] (rule3) {$\underbar{z}_l$};
    \node [neu, right = of rule3] (rule4) {$\underbar{z}_r$};
    %consequent
    \node [neu, above right = 0.8 and 0.4 of rule2] (consequent) {$O{f_m}$};
    %sum
    \node [sum, above = of consequent] (sum) {\tiny+};
    %integral
    \node [blockk, above = of sum] (integral) {$D_t^{-q}$};
    %sum1
    \node [sum, above = of integral] (sum1) {};

    \node[above=-2pt] at (sum1.center){\tiny $+$};
    \node[below=-2pt] at (sum1.center){\tiny $-$};
    %
    \node [input,right = of sum, name=input5] {};
    %
    \node [input,above = of sum1, name=input6] {};
    %
    \node [input,below = of neu1, name=input2] {};
    \node [input,below = of neu2, name=input3] {};
    \node [input,below = of neu3, name=input4] {};
\draw [draw,-&gt;] (input1) -- node {\textcolor{blue}{$\tt\hat{y}(t)$}} (neu);
\draw [draw,-&gt;] (input2) -- node {\textcolor{blue}{$\tt\hat{y}(t-\tau)$}} (neu1);
\draw [draw,-&gt;] (input3) -- node {\textcolor{blue}{$\tt\hat{y}(t-2\tau)$}} (neu2);
\draw [draw,-&gt;] (input4) -- node {\textcolor{blue}{$\tt\hat{y}(t-3\tau)$}} (neu3);

\draw [draw,-&gt;] (neu) -- node [left]{$\bar{u}$} (membership1);
\draw [draw,-&gt;] (neu) -- node [right]{$\underbar{u}$} (membership2);
\draw [draw,-&gt;] (neu1) -- (membership3);
\draw [draw,-&gt;] (neu1) -- (membership4);
\draw [draw,-&gt;] (neu2) -- (membership5);
\draw [draw,-&gt;] (neu2) -- (membership6);
\draw [draw,-&gt;] (neu3) -- (membership7);
\draw [draw,-&gt;] (neu3) -- (membership8);

\draw [draw,-&gt;] (membership1) -- (rule1);
\draw [draw,-&gt;] (membership3) -- (rule1);
\draw [draw,-&gt;] (membership5) -- (rule1);
\draw [draw,-&gt;] (membership7) -- (rule1);
%
\draw [draw,-&gt;] (membership2) -- (rule2);
\draw [draw,-&gt;] (membership4) -- (rule2);
\draw [draw,-&gt;] (membership6) -- (rule2);
\draw [draw,-&gt;] (membership8) -- (rule2);
%
\draw [draw,-&gt;,red] (membership1) -- (rule3);
\draw [draw,-&gt;,red] (membership3) -- (rule3);
\draw [draw,-&gt;,red] (membership5) -- (rule3);
\draw [draw,-&gt;,red] (membership7) -- (rule3);    
%
\draw [draw,-&gt;,red] (membership2) -- (rule4);
\draw [draw,-&gt;,red] (membership4) -- (rule4);
\draw [draw,-&gt;,red] (membership6) -- (rule4);
\draw [draw,-&gt;,red] (membership8) -- (rule4);
%
\draw [draw,-&gt;] (rule1) -- (consequent);
\draw [draw,-&gt;] (rule2) -- (consequent);
\draw [draw,-&gt;] (rule3) -- (consequent);
\draw [draw,-&gt;] (rule4) -- (consequent);
%
\draw [draw,-&gt;] (consequent) -- (sum);
%
\draw [draw,-&gt;] (sum) -- (integral);
%
\draw [draw,-&gt;] (integral) -- (sum1);
%
\draw [draw,-&gt;] (input5) -- (sum);
%    
\draw [draw,-&gt;] (input6) -- (sum1);
%
\draw[double,dashed,-,green](sum1)--(5.5,11.1)-- ([yshift=-0.5em]consequent.south east);



\end{tikzpicture}
\end{adjustbox}
\caption{Online identification structure.}\label{fig30}
\end{figure}

Welcome to TSE. Please post a Minimal Working Example, instead of a code snippet. — José Carlos Santos, Apr 07 '23 at 13:54

Jasper Habicht · Accepted Answer · 2023-04-10T16:08:29.387

You could use the picture path option to place a plotted function inside a node:

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
\tikzset{
    neu/.style={
        draw,
        fill=blue!20,
        circle,
        minimum size=0.5cm,
    },
    declare function={
        sigma(\x) = 1/(1+exp(-\x));
    }
}
\node[neu, path picture={
    \draw[shift={(path picture bounding box.center)},
        domain=-0.3:0.3, samples=50,
    ] plot ({\x},{0.3(sigma(30\x)-0.5)});
}] (membership1) {};
\end{tikzpicture}
\end{document}

For your concrete case, you could do something like this:

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
\tikzset{
    neu/.style={
        draw,
        fill=blue!20,
        circle,
        minimum size=0.5cm,
    },
    declare function={
        sigma(\x) = 1/(1+exp(-\x));
        sigmap(\x) = sigma(\x)*(1-sigma(\x));
    }
}
\node[neu, path picture={
    \draw[blue, shift={(path picture bounding box.center)},
        domain=-0.25:0.25, samples=50,
    ] plot ({\x},{0.3(sigma(30\x-2)-0.5)});
    \draw[blue, shift={(path picture bounding box.center)},
        domain=-0.25:0.25, samples=50
    ] plot ({\x},{0.3(sigma(20\x+0.5)-0.5)});
}] at (0,0) (membership1) {};
\node[neu, path picture={
    \draw[blue, shift={(path picture bounding box.center)},
        domain=-0.25:0.25, samples=50,
    ] plot ({\x},{0.3(sigma(-30\x-2)-0.5)});
    \draw[blue, shift={(path picture bounding box.center)},
        domain=-0.25:0.25, samples=50
    ] plot ({\x},{0.3(sigma(-20\x+0.5)-0.5)});
}] at (2,0) (membership2) {};
\node[neu, path picture={
    \draw[red, shift={(path picture bounding box.center)},
        domain=-0.25:0.25, samples=50,
    ] plot ({\x},{(sigmap(20*\x)-0.1)});
}] at (1,0) (membership3) {};
\end{tikzpicture}
\end{document}

Thank you for your answer but I want it to look like an interval as shown in the image. Is there a way to draw two lines as depicted? — Milito, Apr 07 '23 at 21:30
@Milito Sure, you can add as many plots as you wish (see my edit). I don't know the function for these plots though. — Jasper Habicht, Apr 09 '23 at 16:21

How to draw sigmoid function in flowchart block in latex

1 Answers1