Como posicionar relativamente no tikz?

Question

Estou tentando desenhar um diagrama de controle com tikz e tenho algumas dúvidas a respeito:

• Como pode ser removida a fronteira da perturbação?
• Como posicionar à esquerda e à direita os nós Custo e Restrições?

\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

Como posso me aproximar y(n)mais do Predict rectangle, para estar alinhado comu(n)

Eu tentei o seguinte, com o resultado acima.

\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. Ou talvez definir um novo estilo de nó sem desenhar a borda?

2. Muitas possibilidades aqui, dependendo do resultado desejado. Você pode usar, por exemplo below right, below lefte ajustar o posicionamento usando âncoras, turnos. Se a positioningbiblioteca foi carregada, você pode usar algo como below left=10pt and 20pt of <name>(veja o segundo exemplo de código abaixo).

O 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}

Algumas observações:

1. Por favor, mude de of=para =ofusar a positioningbiblioteca.

2. Mudar de \tikzstylepara \tikzset.

3. Você não pode colocar um flutuador como figuredentro tikzpicture; você pode fazer isso do outro lado.

4. Seu fator de escala parece um pouco baixo.

O 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 a nova pergunta após a edição da pergunta original: a ideia é nomear um nó para o primeiro rótulo e então usar o sistema de coordenadas perpendiculares para colocar o outro rótulo na mesma coordenada x. O código de exemplo a seguir ilustra isso:

\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}