同时使用external和会导致\pgfmathdeclarefunction
! Illegal parameter number in definition of \pgfmathfloat@expression.
! Package PGF Math Error: Could not parse input '' as a floating point number, sorry. The unreadable part was near ''. (in '##1').
这是一个 MWE
\documentclass{article}
\usepackage{pgfplots}\usetikzlibrary{external}
\begin{document}
\tikzexternalize
\begin{tikzpicture}
\pgfmathdeclarefunction{f}{1}{\pgfmathparse{#1}}
\begin{axis}
\addplot {f(x)};
\end{axis}
\end{tikzpicture}
\end{document}
是什么导致了这些问题？我该如何解决？