Writing equations inside rectangle in Tikz

Question

I am trying to draw the diagram in the attached picture. I have not been able to accomplish two tasks after several hours. Thank you for your help

Write the equation shown below in the plant rectangle box.

   \dot{x} = f(x, \alpha(x, \theta)) \\
   y = h(x)
\end{align*}

Attach a straight line in the middle of the line joining the "sum" and "times" node as shown in the attached picture.

The Figure I am trying to draw:

My current result

My code

\usepackage{tikz}
\usetikzlibrary{positioning}
\usetikzlibrary{arrows}
\usetikzlibrary{backgrounds,fit,shapes}
\begin{document}
\begin{figure}[ht]
    \centering
        \begin{tikzpicture}
        % Sum shape
    \node[draw=black, 
        circle,
        minimum size=0.8cm,
       % fill=green!10
        ] (sum) at (0,0){$\large + $};

        % Integrator
        \node [draw=black, 

%    fill=green, 
            minimum width=1.5cm, 
             minimum height=1.2cm,
              right=1cm of sum,
            ] (Integrator) {\large $\frac{k}{s}$};
     % low pass filter
        \node [draw=black, 

%    fill=green, 
            minimum width=1.5cm, 
             minimum height=1.2cm,
              right=1cm of Integrator,
            ] (lowfilter) {\large $\frac{\omega_l}{s + \omega_l}$};
  % times shape
    \node[draw=black, 
        circle,
        minimum size=0.8cm,
        right=1cm of lowfilter,
        ] (times){$\large \times$} ;

         % High pass filter
        \node [draw=black, 

%    fill=green, 
            minimum width=1.5cm, 
             minimum height=1.2cm,
              right=1.5cm of times,
            ] (highfilter) {\large $\frac{s}{s + \omega_h}$};
%======================================================================
% I want to write equation inside this rectangle
%\begin{align}
 %   \dot{x} = f(x, \alpha(x, \theta)) \
%    y = h(x)
%\end{align}
        % Plant
            \node [draw=black, 
%    fill=green, 
            minimum width=4cm, 
             minimum height=2cm,
              above=2cm of times,
            ] (plant) {\large $\dot{x} = f(x, \alpha(x, \theta))  $ };

           % ] (plant) {\begin{align}
           %    \dot{x} = f(x, \alpha(x, \theta))
         %   \end{align}}; % $\dot{x} = f(x, \alpha(x, \theta))  $ };
\draw[-stealth] (highfilter.west) -- (times.east)
node[midway,above]{$y -\eta $};

 \draw[-stealth] (times.west) -- (lowfilter.east);

% node[midway,above]{};
\draw[-stealth] (lowfilter.west) -- (Integrator.east)
node[midway,above]{$\xi$};

  \draw[-stealth] (Integrator.west) -- (sum.east)
node[midway,above]{$\hat{\theta}$};

    \draw[-stealth] (sum.north) |-  (plant.west);


\draw[-stealth] (plant.east) -- ++ (4,0) 
    nodenear end{}node[near end,above]{$y$};
   \draw[-stealth] (output.center) |-  (highfilter.east);

   \draw[stealth-stealth] (times.south) --++ (0, -1) -| (sum.south)
   node[midway](connector){};

   %\draw[-stealth] (connector.center) --++ (0, -1);




    \end{tikzpicture}
\caption{Caption}
\label{fig:my_label}

\end{figure}
\end{document}

Use aligned instead of align (or gathered if you don't want alignment), i.e. the inline versions of the math environments. You could also specify a text width for the node which would make the "normal" environments work again but I don't see a reason to do it that way. — Qrrbrbirlbel, Dec 20 '22 at 18:15
I'd argue, this is all covered in Q1342 unless you have a follow-up. — Qrrbrbirlbel, Dec 20 '22 at 18:17
Add coordinate[near start, pin=below:{$\alpha\sin \omega t$}] between -| and (sum.south). If it complains, give the coordinate a name. (Or just use a named coordinate and draw a separate line and node in relation to it.) — Qrrbrbirlbel, Dec 20 '22 at 18:51

Zarko · Accepted Answer · 2022-12-20T22:20:57.013

Like this:

The simplest way to write plant equation system is use aligned environment of amsmath package. I took a liberty and define styles for scheme elements and sightly redesign its input part. By this scheme code is shorter and (hopefully) more clear.

Edit: added is missing input part of scheme.

%\documentclass{article}
\documentclass[margin=3mm]{standalone}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,
                backgrounds,
                fit,
                positioning,
                quotes}
\newcommand\ppbb{path picture bounding box}
\begin{document}
%    \begin{figure}[ht]
%    \centering
\begin{tikzpicture}[auto=right,
    node distance = 8mm and 12mm,
       dot/.style = {circle, fill, minimum size=3pt, inner sep=0pt,
                     node contents={}},
shorten <>/.style = {shorten <=#1, shorten >=#1},
       sum/.style = {circle, draw=black, minimum size=6mm,
                     path picture={\draw[very thick,shorten <>=1mm]
                        (\ppbb.north) edge[-] (\ppbb.south)
                        (\ppbb.west)  -- (\ppbb.east);},
                    node contents={}},
                % Sum shape
       mul/.style = {circle, draw=black, minimum size=6mm,
                     path picture={\draw[very thick,shorten <>=1mm]
                        (\ppbb.north west) edge[-] (\ppbb.south east)
                        (\ppbb.south west) -- (\ppbb.north east);},
                    node contents={}},
         N/.style = {draw, minimum size=12mm, align=center, font=\large},
every edge/.append style = {draw, -Stealth}
                ]
% blocks
\node (sum) [sum];
\node (int) [N, right=of sum]   {$\frac{k}{s}$};
\node (LPF) [N, right=of int]   {$\frac{\omega_l}{s + \omega_l}$};
\node (mul) [mul, right=of LPF];
\node (HPF) [N, right=of mul]   {$\frac{s}{s + \omega_h}$};
%
\node (plant) [N, above=of mul] {$\begin{aligned}  % <----
                                 \dot{x} & = f(x, \alpha(x,\theta))\
                                      y & = h(x)
                                \end{aligned}$};
\node (out) [dot, right=of plant-| HPF.east, label=$y$];
%
\node (in) [dot, below=of sum];
%% lines
\path   (HPF) edge["$y-\eta$"]          (mul)
        (mul) edge (LPF)
        (LPF) edge["$\xi$"]             (int)
        (int) edge["$\hat{\theta}$"]    (sum)
        (in)  edge   (sum)
        (out) edge ++ (1.2,0);
%
\draw[-Stealth] (sum) |- (plant) node[pos=0.9, above] {$\theta$};
\draw[-Stealth] (plant) -- (out) |- (HPF);
%
\draw   (in) to["$a\sin\omega t$"] ++ (-2,0);
\draw[-Stealth] (in) -| (mul);
\end{tikzpicture}
%    \caption{Caption}
%    \label{fig:my_label}
%    \end{figure}
\end{document}

Writing equations inside rectangle in Tikz

1 Answers1