所以，我是 Tikz/PGF 的新手，我正在嘗試繪製一張圖像，顯示速度隨時間和距離的變化。
藍線顯示物體首先具有到達某一點的線速度（函數 υ=χ*τ）。紅線顯示物件以常數 a=1 減速（函數 x= υ0t - ½ αt^2）。當我實現減速函數時，紅色曲線不沿著時間軸移動 t（或 y 軸），儘管它會改變速度（應該趨向於 0）和距離（會增長）。我究竟做錯了什麼？預先感謝您的提示和解決方案！
\documentclass[border=45pt]{standalone}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
\usepackage{pgfmath}
\usepackage{amsmath}
\usepackage{tikz-3dplot}
\pgfplotsset{compat=newest}
\begin{document}
\begin{tikzpicture} [
% Define Time with Constant Speed Function
declare function={
linear(\x,\u,\t)= \x / \u;},
%Define Breaking / Deceleration Function with a=1
declare function={
curve(\x,\u,\t)= (\u * \t -(1/2 * 1 * \t^2));}
]
\begin{axis}[
%view={90}{60},
no markers,
zmin=0, zmax=10,
xmin=0, xmax=10,
ymin=0,ymax=10,
xtick={3},
xticklabels={$u_0$},
ytick={2},
yticklabels={$t_{safe}$},
ztick={6},
zticklabels={$x_{MP}$},
axis lines=middle,
zlabel=$x$, zlabel style={at={(rel axis cs:0,0,1)}, anchor=east},
xlabel=$u$, xlabel style={at={(rel axis cs:1,0,0)}, anchor=west},
ylabel=$t$, ylabel style={at={(rel axis cs:0,1,0)}, anchor=south west}
]
%dashed Tsafe
\draw[dashed] (6,2,0)--(0,2,0); % change middle variable = y to move line on y = t axis, also move ticks on above set
%grayrectangle on Tsafe
\fill[fill=gray!13,opacity=0.8] (0,2,0) -- (6,2,0) -- (6,2,6) -- (0,2,6) -- (0,2,0); % change middle variable = y to adjust plane on tsafe axis
%grayrectangle on Xmp
\fill[fill=gray!15, opacity=0.8] (0,0,6) -- (0,4,6) -- (6,4,6)-- (6,0,6) -- (0,0,6); % if MP point changes, change right variable = z to move plane on z = x axis, also move ticks on above set
\addplot3 [blue!50!black, thick,domain=0:1] (3,x, {linear(x,3,0)}); %point (x,u,t) = (3m,3m/s,1s)
\addplot3 [red!50!black,thick,domain=0:3] (3-y,1,{curve(3,5,y)});
\end{axis}
\end{tikzpicture}
\end{document}