¿Cómo posicionar en tikz relativamente?

Question

Estoy intentando dibujar un diagrama de control con tikz y tengo algunas preguntas al respecto:

• ¿Cómo se puede eliminar la frontera de la perturbación?
• ¿Cómo se pueden colocar a izquierda y derecha los nodos de Costo y Restricciones?

\tikzstyle{controller} = [draw, fill=blue!20, rectangle, 
minimum height=3em, minimum width=6em]
\tikzstyle{block} = [draw, fill=yellow!20, rectangle, 
minimum height=3em, minimum width=6em]

\tikzstyle{disturbance} = [draw, node distance=1.5cm, line width=0pt]    
\tikzstyle{sum} = [draw, circle, node distance=1.5cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]
\begin{figure}[!]
\centering
\begin{tikzpicture}[auto, node distance=3cm,>=latex', scale=0.5 ,every
node/.style={transform shape}]      
    % We start by placing the blocks
    \node [input, name=input] {};
    \node [sum, right of=input] (sum) {};
    \node [controller, right of=sum] (controller) {Controller};
    \node [block, right of=controller, node distance=4cm] (system) {System};
    \node [disturbance, name=disturbance, above of=system] {Disturbance};
    \node [disturbance, name=costfunc, below of=system,] {Cost};
    \node [disturbance, name=constraint, below of=system] {Constraints};
    % We draw an edge between the controller and system block to 
    % calculate the coordinate u. We need it to place the measurement block. 
    \draw [->] (controller) -- node[name=u] {$u(n)$} (system);
    \node [output, right of=system] (output) {};        

    % Once the nodes are placed, connecting them is easy. 
    \draw [draw,->] (input) -- node {$r(n)$} (sum);
    \draw [->] (sum) -- node {$e(n)$} (controller);
    \draw [->] (disturbance) -- (system);
    \draw [->] (system) -- node [name=y] {$y(n)$}(output);
    \draw [->] (y) |-  ($(y.south) + (0,-2)$) -| node[pos=0.99]
    {$-$} node [near end] {$y(n)$} (sum);
\end{tikzpicture}   
\label{fig:mpc_bloc_diagram}
\end{figure}

---

EDITADO

¿Cómo puedo acercarme más y(n)al Predict rectangle, para alinearme con?u(n)

Intenté lo siguiente, con el resultado anterior.

\draw [->] (y) |- node [near end] {$y(n)$} ($(predict.east)+(0,0.35)$);
\draw [->] (u) |- node [near end] {$u(n)$} ($(predict.east)+(0,-0.35)$);

Answer 1

1. draw=none. ¿O quizás definir un nuevo estilo de nodo sin dibujar el borde?

2. Aquí hay muchas posibilidades, dependiendo del resultado deseado. Puede utilizar, por ejemplo below right, below lefty ajustar el posicionamiento mediante anclajes y cambios. Si la positioningbiblioteca se ha cargado, puede usar algo como below left=10pt and 20pt of <name>(consulte el segundo código de ejemplo a continuación).

El código:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc,arrows}

\begin{document}

\tikzstyle{controller} = [draw, fill=blue!20, rectangle, 
minimum height=3em, minimum width=6em]
\tikzstyle{block} = [draw, fill=yellow!20, rectangle, 
minimum height=3em, minimum width=6em]

\tikzstyle{disturbance} = [draw, node distance=1.5cm, line width=0pt]    
\tikzstyle{sum} = [draw, circle, node distance=1.5cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]
\begin{figure}
\centering
\begin{tikzpicture}[auto, node distance=3cm,>=latex', scale=1.5 ,every
node/.style={transform shape}]      
    % We start by placing the blocks
    \node [input, name=input] {};
    \node [sum, right of=input] (sum) {};
    \node [controller, right of=sum] (controller) {Controller};
    \node [block, right of=controller, node distance=4cm] (system) {System};
    \node [disturbance, draw=none,name=disturbance, above of=system] {Disturbance};
    \node [disturbance, name=costfunc, below left of=system,] {Cost};
    \node [disturbance, name=constraint, below right of=system] {Constraints};
    % We draw an edge between the controller and system block to 
    % calculate the coordinate u. We need it to place the measurement block. 
    \draw [->] (controller) -- node[name=u] {$u(n)$} (system);
    \node [output, right of=system] (output) {};        

    % Once the nodes are placed, connecting them is easy. 
    \draw [draw,->] (input) -- node {$r(n)$} (sum);
    \draw [->] (sum) -- node {$e(n)$} (controller);
    \draw [->] (disturbance) -- (system);
    \draw [->] (system) -- node [name=y] {$y(n)$}(output);
    \draw [->] (y) |-  ($(y.south) + (0,-2)$) -| node[pos=0.99]
    {$-$} node [near end] {$y(n)$} (sum);
\end{tikzpicture}   
\label{fig:mpc_bloc_diagram}
\end{figure}

\end{document}

Algunos comentarios:

1. Cambie de of=usar =ofla positioningbiblioteca.

2. Cambiar de \tikzstylea \tikzset.

3. No puedes colocar un flotador como figureen el interior tikzpicture; Puedes hacerlo al revés.

4. Su factor de escala parece un poco bajo.

El código:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc,arrows,positioning}

\tikzset{
controller/.style={
  draw, 
  fill=blue!20, 
  rectangle, 
  minimum height=3em, 
  minimum width=6em
  },
block/.style={
  draw, 
  fill=yellow!20, 
  rectangle, 
  minimum height=3em, 
  minimum width=6em
  },
disturbance/.style={
  draw, 
  line width=0pt
  },    
sum/.style={
  draw, 
  circle, 
  node distance=1.5cm
  },
input/.style={coordinate},
output/.style={coordinate}
}

\begin{document}

\begin{figure}
\centering
\begin{tikzpicture}[
  auto, 
  node distance=1.5cm,
  >=latex', 
  scale=0.5 ,
  every node/.style={transform shape}
]      
    % We start by placing the blocks
    \node [input, name=input] {};
    \node [sum, right =of input] (sum) {};
    \node [controller, right =of sum] (controller) {Controller};
    \node [block, right =of controller, node distance=4cm] (system) {System};
    \node [disturbance, draw=none,name=disturbance, above = 20pt of system] {Disturbance};
    \node [disturbance,draw=none,name=costfunc, below left = 20pt and 0pt of system,anchor=east] {Cost};
    \node [disturbance,draw=none,name=constraint, below right = 20pt and 15pt of system,anchor=east] {Constraints};
    % We draw an edge between the controller and system block to 
    % calculate the coordinate u. We need it to place the measurement block. 
    \draw [->] (controller) -- node[name=u] {$u(n)$} (system);
    \node [output, right =of system] (output) {};        

    % Once the nodes are placed, connecting them is easy. 
    \draw [draw,->] (input) -- node {$r(n)$} (sum);
    \draw [->] (sum) -- node {$e(n)$} (controller);
    \draw [->] (disturbance) -- (disturbance|-system.north);
    \draw [->] (system) -- node [name=y] {$y(n)$}(output);
    \draw [->] (y) |-  ($(y.south) + (0,-2)$) -| node[pos=0.99]
    {$-$} node [near end] {$y(n)$} (sum);
\end{tikzpicture}   
\label{fig:mpc_bloc_diagram}
\end{figure}

\end{document}

Para la nueva pregunta después de la edición de la pregunta original: la idea es nombrar uno como nodo para la primera etiqueta y luego usar el sistema de coordenadas perpendiculares para colocar la otra etiqueta en la misma coordenada x. El siguiente código de ejemplo ilustra esto:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc,arrows,positioning}

\tikzset{
controller/.style={
  draw, 
  fill=blue!20, 
  rectangle, 
  minimum height=3em, 
  minimum width=6em
  },
block/.style={
  draw, 
  fill=yellow!20, 
  rectangle, 
  minimum height=3em, 
  minimum width=6em
  },
disturbance/.style={
  draw, 
  line width=0pt
  },    
sum/.style={
  draw, 
  circle, 
  node distance=1.5cm
  },
input/.style={coordinate},
output/.style={coordinate}
}

\begin{document}

\begin{tikzpicture}[
  auto, 
  node distance=1.5cm,
  >=latex', 
  every node/.style={transform shape}
]      
  \node [controller] (nodea) {Some node a};
  \node [controller, right =of nodea] (nodeb) {Some node b};
  \node [controller, above left =of nodea] (nodec) {Some node c};

  \draw [->] 
    (nodea) |- 
      node [near end] (un) {$u(n)$}
  ($(nodec.east)+(0,-0.35)$);
  \draw [->] 
    (nodeb) |- 
      coordinate[near end] (aux) 
  ($(nodec.east)+(0,0.35)$) node[above] at (un|-aux) {$y(n)$};
\end{tikzpicture}   

\end{document}