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Tikz 与 foreach

tag-icon • tag-icon tikz-pgf foreach gnuplot
Tikz 与 foreach

大家好，我想绘制一个具有 1 个变量及其总和的函数，因此基本上我的函数是这样的：

sum(11/(2*k-1)*sin(2*50*\%pi*(2*k-1)*x)

我想用 Gnuplot 来实现它，但它给了我一个错误消息：

Package pgfplots Error: Sorry, the gnuplot-result file 'test.pgf-plotlot <file>.gnuplot' manually on the respective gnuplot file.. }


\documentclass{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    xlabel = $t$,
    xtick = {-.5,.5},
    xticklabels = {$-\frac{T}{2}$, $\frac{T}{2}$},
    ytick = {-1,-.5,.5,1},
    yticklabels = {$-A$, $-\frac{A}{2}$, $\frac{A}{2}$, $A$},
    domain = -.75:.75,
    samples = 200,
    ]
    \addplot[mark = none] gnuplot {(x - floor(x +.5)) < 0 ? -1 : 1};
    \addlegendentry{Signal}
    \foreach \i in {2,4,6,8}{%
      \addplot+[mark = none] gnuplot[raw gnuplot] {%
        set samples 200;
        fourier(k, x) = (11 /(2*k-1)*sin(2*50*\%pi*(2*k-1)*x)
        plot[-.75:.75] sum [k=0:\i] fourier(k,x)};
      \addlegendentryexpanded{\number\numexpr 2*\i+1\relax{} first terms}
    }
  \end{axis}
\end{tikzpicture}
\end{document}

答案1

gnuplot 代码中有一些错误。它应该是pi而不是\%pi，并且在 的定义后缺少右括号和分号fourier。我删除了 的外括号fourier并添加了分号。

% arara: pdflatex: { shell: yes }
\documentclass{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    xlabel = $t$,
    xtick = {-.5,.5},
    xticklabels = {$-\frac{T}{2}$, $\frac{T}{2}$},
    ytick = {-1,-.5,.5,1},
    yticklabels = {$-A$, $-\frac{A}{2}$, $\frac{A}{2}$, $A$},
    domain = -.75:.75,
    samples = 200,
    ]
    \addplot[mark = none] gnuplot {(x - floor(x +.5)) < 0 ? -1 : 1};
    \addlegendentry{Signal}
    \foreach \i in {2,4,6,8}{%
      \addplot+[mark = none] gnuplot[raw gnuplot] {%
        set samples 200;
        fourier(k, x) = 11 /(2*k-1)*sin(2*50*pi*(2*k-1)*x);
        plot[-.75:.75] sum [k=0:\i] fourier(k,x);
      };
      \addlegendentryexpanded{\number\numexpr 2*\i+1\relax{} first terms}
    }
  \end{axis}
\end{tikzpicture}
\end{document}

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