矢量场中的 0 矢量

Question

我正在尝试绘制一个带有 5 x 5 个箭头（总共 25 个）的矢量场。它看起来不错，除了它任意选择“向上”作为 0 矢量的方向。我怎样才能让它完全不显示 0 长度的箭头？

我的代码：

\documentclass{article}
\tikzset{>=stealth} 
\usepackage{tikz}
\usepackage{pgfplots} 
\begin{document}
\begin{tikzpicture}

\draw[->, thick] (-3,0)--(3,0) node[right] {$x$};
\draw[->, thick] (0,-3)--(0,3) node[above] {$y$};

\def\factor{0.15}
\foreach \x in {-2.5,-2,...,2.5} {
    \foreach \y in {-2.5,-2,...,2.5}{
            \draw[->] (\x,\y)--++(\factor*\y,-\factor*\x);
    }
}
\end{tikzpicture}
\end{document}

结果（注意原点的箭头）：

Answer 1

一种可能性是\ifthenelse：

\documentclass{article}

\usepackage{tikz}
\usepackage{pgfplots} 
\usepackage{ifthen}
\tikzset{>=stealth} 
\begin{document}
\begin{tikzpicture}

\draw[->, thick] (-3,0)--(3,0) node[right] {$x$};
\draw[->, thick] (0,-3)--(0,3) node[above] {$y$};

\def\factor{0.15}
\foreach \x in {-2.5,-2,...,2.5} {
    \foreach \y [evaluate=\y as \r using int(ceil(abs(\x)+abs(\y)))] in {-2.5,-2,...,2.5}{
            \ifthenelse{\r=0}{}{\draw[->] (\x,\y)--++(\factor*\y,-\factor*\x);}
    }
}
\end{tikzpicture}
\end{document}

Answer 2

投入几项\ifx检查以确认其为零。

\documentclass{article}
\usepackage{tikz}
\usepackage{pgfplots} 
\tikzset{>=stealth} 
\newcommand*\zero{0}
\begin{document}
\begin{tikzpicture}

\draw[->, thick] (-3,0)--(3,0) node[right] {$x$};
\draw[->, thick] (0,-3)--(0,3) node[above] {$y$};

\def\factor{0.15}
\foreach \x in {-2.5,-2,...,2.5} {
    \foreach \y in {-2.5,-2,...,2.5}{
     \def\tmp{\draw[->] (\x,\y)--++(\factor*\y,-\factor*\x)}
     \ifx\zero\x\ifx\zero\y\else\tmp\fi\else\tmp\fi;
    }
}
\end{tikzpicture}
\end{document}

Answer 3

\foreach由于舍入问题，最好避免在 中使用小数。您可以测试\x和是否都\y为零：

\documentclass{article}
\usepackage{tikz}

\tikzset{>=stealth} 

\begin{document}

\begin{tikzpicture}

\draw[->, thick] (-3,0)--(3,0) node[right] {$x$};
\draw[->, thick] (0,-3)--(0,3) node[above] {$y$};

\def\factor{0.15}
\foreach \x in {-5,-4,...,5} {
  \foreach \y in {-5,-4,...,5}{
    \pgfmathparse{ifthenelse(and(\x==0,\y==0),1,0)}
    \ifnum\pgfmathresult=0
      \draw[->] (\x/2,\y/2)--++(\factor*\y/2,-\factor*\x/2);
    \fi
  }
}
\end{tikzpicture}

\end{document}