PGF 数学错误：抱歉，浮点单元的内部例程得到了格式错误的浮点数

Question

我有下面这段代码，尽管我可以使用 pgfplots 来实现相同的目标，但由于遗留原因，大多数 tikz 代码都是这样的。

  \begin{tikzpicture}
    \pgfkeys{/pgf/fpu=true,
             /pgf/fpu/output format=fixed
    }
    % low pass
    \draw[->] (0,0) -- (0,2) node[left] {$V$};
    \draw[->] (-0.5,0) -- (4,0) node[below] {$f$};

    \draw[line width=1pt, domain=0:4, smooth,
    blue,samples=1000] plot ({\x},{1/(1+(\x/2)^24)}); \draw
    (3,1.5) node[] {lowpass};
 \end{tikzpicture}

上面的编译出现以下错误：

! Package PGF Math Error: Sorry, an internal routine of the floating point unit
 got an ill-formatted floating point number `-56.90549000000000'. The unreadabl
e part was near '-56.90549000000000'..

使用了以下包和库：

\usepackage{graphicx,tikz,pgfplots,float}
\usetikzlibrary{arrows,shapes,er,intersections,decorations,positioning,shapes.geometric,matrix,decorations.pathreplacing,calc}

错误原因是什么？

Answer 1

该密钥/pgf/fpu=true破坏了大部分 TikZ 绘图代码，因为解析和格式化之间没有分离，另请参阅https://github.com/pgf-tikz/pgf/issues/678。

但是，您始终可以尝试在本地使用/pgf/fpu=true导致问题的单一路径，Dimension too large并祈祷它不会破坏其他任何东西。

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{fpu}
\begin{document}

\begin{tikzpicture}
  % low pass
  \draw[->] (0,0) -- (0,2) node[left] {$V$};
  \draw[->] (-0.5,0) -- (4,0) node[below] {$f$};

  \draw[line width=1pt,domain=0:4,smooth,blue,samples=1000,/pgf/fpu=true,/pgf/fpu/output format=fixed] plot ({\x},{1/(1+(\x/2)^24)});
  \draw (3,1.5) node[] {lowpass};
\end{tikzpicture}

\end{document}

$ bench "pdflatex test.tex"
benchmarking pdflatex test.tex
time                 1.387 s    (1.226 s .. 1.550 s)
                     0.998 R²   (0.993 R² .. 1.000 R²)
mean                 1.310 s    (1.252 s .. 1.356 s)
std dev              58.24 ms   (26.01 ms .. 76.84 ms)
variance introduced by outliers: 19% (moderately inflated)

但是如果你只想绘制曲线的示意图，我建议你使用贝塞尔曲线来获得平滑的拐角。这看起来几乎完全相同，但不会使文档的编译时间激增。

\documentclass{article}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}
  % low pass
  \draw[->] (0,0) -- (0,2) node[left] {$V$};
  \draw[->] (-0.5,0) -- (4,0) node[below] {$f$};

  \draw[line width=1pt,blue] (0,1) -- (1.5,1) .. controls (2.2,1) and (1.8,0) .. (2.5,0) -- (4,0);
  \draw (3,1.5) node[] {lowpass};
\end{tikzpicture}

\end{document}

$ bench "pdflatex test.tex"
benchmarking pdflatex test.tex
time                 292.8 ms   (277.8 ms .. 302.3 ms)
                     0.999 R²   (NaN R² .. 1.000 R²)
mean                 298.0 ms   (292.9 ms .. 300.7 ms)
std dev              4.747 ms   (1.946 ms .. 6.257 ms)
variance introduced by outliers: 16% (moderately inflated)