负数学表达式坐标

Question

我只创建这个：

有了这个：

\documentclass{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
  \begin{axis}[ 
  axis x line=bottom,
  axis y line=left,
  ultra thick,
  y coord trafo/.code={\pgfmathparse{sqrt(#1)}},
  y coord inv trafo/.code={\pgfmathparse{pow(#1,2)}}
  ] 
    \addplot coordinates {
    (0,0)
    (0.3,0)
    (0.44,0.00016)
    (0.45,0.00045)
    (0.49,0.00071)
    (0.5,0.001)
    (0.51,0.00139)
    (0.54,0.00176)
    (0.56,0.00214)
    (0.57,0.00243)
    (0.61,0.00279)
    (0.63,0.00327)
    (0.64,0.00386)
    (0.67,0.00433)
        };
        \end{axis}
        \end{tikzpicture}
        \end{document}

但我需要输入负坐标，例如：（-0.51，-0.00139）

我还需要红线和文字（I，V）：

Answer 1

• 通过设置axis lines=middle，一旦添加负坐标，两个轴都会位于中间。
• 您可以使用xlabel=$V$和添加标签ylabel=$I$。
• 可以使用 将这些标签放置在相对于轴的不同位置x label style={at={(current axis.right of origin)}, anchor=west}。
• 可以使用 绘制红线\draw[red, dashed] (axis cs:0.6, 0)--(axis cs:0.6, 0.004);。这里我使用axis cs坐标，即链接到轴的坐标。
• 您的最后一个请求无法实现。您无法在 y 轴上添加负值，因为您使用平方根重新缩放轴。负数的平方根是一个复数。

举个例子，我删除了一些y coord travo东西，并添加了一些负坐标。

平均能量损失

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.14}
\begin{document}
    \begin{tikzpicture}
      \begin{axis}[ 
          axis lines=middle,
          ultra thick,
          xlabel= $V$, ylabel=$I$,
          x label style={at={(current axis.right of origin)}, anchor=west},
%         y coord trafo/.code={\pgfmathparse{sqrt(#1)}},
%         y coord inv trafo/.code={\pgfmathparse{pow(#1,2)}},
          ] 
            \addplot coordinates {
            (-0.48, -0.002)
            (-0.43, -0.0002)
            (-0.3, -0.0001)
            (0,0)
            (0.3,0)
            (0.44,0.00016)
            (0.45,0.00045)
            (0.49,0.00071)
            (0.5,0.001)
            (0.51,0.00139)
            (0.54,0.00176)
            (0.56,0.00214)
            (0.57,0.00243)
            (0.61,0.00279)
            (0.63,0.00327)
            (0.64,0.00386)
            (0.67,0.00433)
             };
         \draw[red, dashed] (axis cs:0.6, 0)--(axis cs:0.6, 0.004);
        \end{axis}
    \end{tikzpicture}
\end{document}

结果