可行區域

Question

我想繪製可行區域。但我不知道該怎麼辦。我需要指導。

\documentclass[tikz, border=5mm]{standalone}

\begin{document}
    
    \begin{tikzpicture}
        
        \draw[gray!50, thin, step=0.5] (-1,-3) grid (5,4);
        \draw[very thick,->] (-1,0) -- (5.2,0) node[right] {$x_1$};
        \draw[very thick,->] (0,-3) -- (0,4.2) node[above] {$x_2$};
        
        \foreach \x in {-1,...,5} \draw (\x,0.05) -- (\x,-0.05) node[below] {\tiny\x};
        \foreach \y in {-3,...,4} \draw (-0.05,\y) -- (0.05,\y) node[right] {\tiny\y};
        
    
        
        \draw (-1,-3) -- node[above,sloped] {\tiny$x_1=-1$} (-1,3);
        
        \draw (0,0) -- node[above,sloped] {\tiny$x_1\leq x_2$} (3,3);
        \draw (0,0) -- node[above,sloped] {\tiny$x_1\leq x_2$} (3,-3);
        \draw (-1,3) -- node[above,sloped] {\tiny$x_2=3$} (3,3);
        \draw (-1,3) -- node[above,sloped] {\tiny$x_2=-3$} (3,3);
        
    \end{tikzpicture}
    
\end{document}

目前結果：

Answer 1

我不確定結果應該是什麼樣子，但這也許可以幫助你。

如果要繪製一個區域，則應該連接代表該區域邊界的線，否則您得到的只是未連接的單條線。另外，如果該區域不應覆蓋圖表的某些部分，則應將其放置在不應覆蓋的區域之前：

\documentclass[tikz, border=10pt]{standalone}

\begin{document}
    
    \begin{tikzpicture}

        \draw[gray!50, thin, step=0.5] (-1,-3) grid (5,4);

        \draw[fill=gray!10]
            (-1,-3) 
                -- node[above, sloped] {\tiny$x_1=-1$} (-1,3)
                -- node[above, sloped] {\tiny$x_2=3$} (3,3)
                -- node[above, sloped] {\tiny$x_1\leq x_2$} (0,0)
                -- node[above, sloped] {\tiny$x_1\leq -x_2$} (3,-3)
                -- node[above, sloped] {\tiny$x_2=-3$} cycle;

        \draw[very thick, ->] (-1,0) -- (5.2,0) node[right] {$x_1$};
        \draw[very thick, ->] (0,-3) -- (0,4.2) node[above] {$x_2$};
        
        \foreach \x in {-1,...,5} 
            \draw (\x,0.05) -- (\x,-0.05) 
            \ifnum\x=0\relax
                node[below right] {\tiny\x}
            \else
                node[below] {\tiny\x}
            \fi ;
        \foreach \y in {-3,...,4} 
            \draw (-0.05,\y) -- (0.05,\y) 
            \ifnum\y=0\else
                node[right] {\tiny\y}
            \fi ;

        \draw[very thick, <->] 
            (0:2) arc[start angle=0, end angle=45, radius=2] 
            node[midway, right] {\tiny$q$};

        \node[align=center] at (3,-2) {unstable \\ region};
        \node[align=center] at (1,-2) {stable \\ region};
        
    \end{tikzpicture}
    
\end{document}

---

刪除大部分標籤和網格後，它更像您顯示的圖片：

\documentclass[tikz, border=10pt]{standalone}

\begin{document}
    
    \begin{tikzpicture}

        \draw[fill=gray!10]
            (-1,-3) -- (-1,3) -- (3,3) -- (0,0) -- (3,-3) -- cycle;

        \draw[very thick, ->] (-1,0) -- (3,0) node[right] {$x_1$};
        \draw[very thick, ->] (0,-3) -- (0,3.5) node[above] {$x_2$};

        \draw[very thick, <->] 
            (0:2) arc[start angle=0, end angle=45, radius=2] 
            node[midway, right] {$q$};

        \node[align=center] at (3,-2) {unstable \\ region};
        \node[align=center] at (1,-2) {stable \\ region};
        
    \end{tikzpicture}
    
\end{document}