我正在尝试在一个图中绘制两个函数。第一个图生成时没有错误。但是当我添加第二个函数的代码时，我得到了错误
Package PGF Math Error: Unknown operator `x' or `x@' (in '.3+.8x').
See the PGF Math package documentation for explanation.
Type H <return> for immediate help.
...
l.22 {.3+.8x};
This error message was generated by an \errmessage
command, so I can't give any explicit help.
Pretend that you're Hercule Poirot: Examine all clues,
and deduce the truth by order and method.
graph/Expected, line 22
Package PGF Math Error: Unknown operator `x' or `x@' (in '.3+.8x').
See the PGF Math package documentation for explanation.
Type H <return> for immediate help.
...
l.22 {.3+.8x};
(That was another \errmessage.)
我正在使用以下代码来获取这两个图：
\usepackage[utf8]{inputenc}
\usepackage{pgfplots}
\pgfplotsset{width=10cm,compat=1.9}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
axis lines = left,
xlabel = \(N\),
ylabel = {\(V\)},
]
%v1 being defined
\addplot[domain=2:10,
samples=100,
color=red,
]
{2-.9/x};
\addlegendentry{\(2-.9/N\)}
%v0 being defined
\addplot[domain=2:10,
samples=100,
color=blue,
]
{.3+.8x};
\addlegendentry{\(.3+.8N\)}
\end{axis}
\end{tikzpicture}
\end{document}
在我看来，第一个和第二个图的代码是相同的，但仍然一起使用它们会出现错误。
我是 Latex 的新手，不知道哪里出了问题。任何帮助我都感激不尽！
谢谢
答案1
乘法不是隐式的，您必须使用*来表示乘法。因此，您需要.3+.8*x，而不是.3+.8x。
在第二个中，您有一个明确的除法运算符，/因此它工作正常。
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{pgfplots}
\pgfplotsset{width=10cm,compat=1.9}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
axis lines = left,
xlabel = \(N\),
ylabel = {\(V\)},
]
%v1 being defined
\addplot[domain=2:10,
samples=100,
color=red,
]
{2-.9/x};
\addlegendentry{\(2-.9/N\)}
%v0 being defined
\addplot[domain=2:10,
samples=2, % <-- you're plotting a straight line, so strictly speaking two samples is enough
color=blue,
]
{.3+.8*x};
\addlegendentry{\(.3+.8N\)}
\end{axis}
\end{tikzpicture}
\end{document}
