Tikz 圖和節點放置

Question

我正在設計一維勢井圖。我正在努力將標籤正確放置在右手線下方。我畫了一條看不見的線並將節點定位在末端。除此之外，如何為紅線之外的區域添加灰色陰影？

乾杯

\documentclass[tikz,border=3.14mm]{standalone} 
    \begin{document} 
        \begin{tikzpicture}
            \draw[-stealth] (-0.5,0) -- (pi,0) node[right]{\(x\)};
            \draw[-stealth] (0,-0.5) -- (0,4) node[above]{\(V(x)\)}; 
            \draw[thick, red, ->, >=stealth] (0,0) -- (0,3) node[left, blue]{\(\)};
            \draw[thick, red,->, >=stealth] (2.5,0) -- (2.5,3);
    %       \node[draw] at (2.5,-0.2)  node[right, black]{\(a\)};
            \draw[line width=0pt] (0,0) -- (2.5,0) node[below, black]{\(a\)};
           \end{tikzpicture} 
       \end{document}  

Answer 1

像這樣

\documentclass[tikz,border=3.14mm]{standalone} 
\begin{document} 
\begin{tikzpicture}
\fill[gray!50] (-.5,-.5) rectangle (pi,4);
\fill[white] (0,0) rectangle (2.5,3);
\draw[-stealth] (-0.5,0) -- (pi,0) node[right]{\(x\)};
\draw[-stealth] (0,-0.5) -- (0,4) node[above]{\(V(x)\)}; 
\draw[thick, red, ->, >=stealth] (0,0) -- (0,3) node[left, blue]{\(x\)};
\draw[thick, red,->, >=stealth] (2.5,0) node[below,black] {$a$} -- (2.5,3);
\end{tikzpicture} 
\end{document}  

注意，如果你想畫一條看不見的線，你不應該使用line width=0pt，因為它仍然大於零。改用\path（其實\draw和\path[draw]是一樣的）：

\path (0,0) -- (2.5,0) node[below, black]{\(a\)};