我修改了代码这里。我试过两种方法。
1.（来源)：
\documentclass{scrartcl}
\usepackage{tikz}
\usepackage[per-mode = fraction]{siunitx}
\usetikzlibrary{datavisualization.formats.functions,
decorations.markings
}
\begin{document}
\begin{tikzpicture}
\datavisualization[scientific axes = {clean,
end labels
},
x axis = {label = $\frac{v}{\si{\cubic\m\per\kg}}$},
y axis = {label = $\frac{p}{\si{\bar}}$},
data/format = function,
visualize as smooth line/.list = {isentropic_press,
isobaric,
isentropic_decompress
},
style sheet = vary dashing,
every visualizer/.style = {decoration = {markings,
mark = at position .5 with {\arrow{>}}
}
},
isentropic_press = {label in legend = {text = isentrope Verdichtung}},
isobaric = {label in legend = {text = isobare Abkühlung}},
isentropic_decompress = {label in legend = {text = isentrope Entspannung}}
]
data[set = isentropic_press] {var x : interval[.5 : 2];
func y = 1 / \value x ^ 1.4;
}
data[set = isobaric] {var x : interval[.5 : 1];
func y = 1 / .5 ^ 1.4;
}
data[set = isentropic_decompress] {var x : interval[1 : 2];
func y = 1 / (\value x - .5) ^ 1.4;%-.5: shifts the function by - 0.5 to the right
}
%accents important points
info {\draw (visualization cs:x = 2,
y = {(1 / 2 ^ 1.4)}
) circle [radius = 1pt]
node [right,
font = \footnotesize
] {1};
}
info {\draw (visualization cs:x = .5,
y = {(1 / .5 ^ 1.4)}
) circle [radius = 1pt]
node [above,
font = \footnotesize
] {2};
}
info {\draw (visualization cs:x = 1,
y = {(1 / .5 ^ 1.4)}
) circle [radius = 1pt]
node [above,
font = \footnotesize
] {3};
}
info {\draw (visualization cs:x = 2,
y = {(1 / 1.5 ^ 1.4)}
) circle [radius = 1pt]
node [right,
font = \footnotesize
] {4};
};
\end{tikzpicture}
\end{document}
2.（来源)：
\documentclass{scrartcl}
\usepackage{tikz}
\usepackage[per-mode = fraction]{siunitx}
\usetikzlibrary{datavisualization.formats.functions,
decorations.markings
}
\begin{document}
\makeatletter
\tikzset{nomorepostaction/.code = {\let\tikz@postactions\pgfutil@empty}}
\makeatother
\begin{tikzpicture}
\datavisualization[scientific axes = {clean,
end labels
},
x axis = {label = $\frac{v}{\si{\cubic\m\per\kg}}$},
y axis = {label = $\frac{p}{\si{\bar}}$},
data/format = function,
visualize as smooth line/.list = {isentropic_press,
isobaric,
isentropic_decompress
},
style sheet = vary dashing,
every visualizer/.style = {postaction = {nomorepostaction,
decorate,
decoration = {markings,
mark = at position .5 with {\arrow{>}}
}
}
},
isentropic_press = {label in legend = {text = isentrope Verdichtung}},
isobaric = {label in legend = {text = isobare Abkühlung}},
isentropic_decompress = {label in legend = {text = isentrope Entspannung}}
]
data[set = isentropic_press] {var x : interval[.5 : 2];
func y = 1 / \value x ^ 1.4;
}
data[set = isobaric] {var x : interval[.5 : 1];
func y = 1 / .5 ^ 1.4;
}
data[set = isentropic_decompress] {var x : interval[1 : 2];
func y = 1 / (\value x - .5) ^ 1.4;%-.5: shifts the function by - 0.5 to the right
}
%accents important points
info {\draw (visualization cs:x = 2,
y = {(1 / 2 ^ 1.4)}
) circle [radius = 1pt]
node [right,
font = \footnotesize
] {1};
}
info {\draw (visualization cs:x = .5,
y = {(1 / .5 ^ 1.4)}
) circle [radius = 1pt]
node [above,
font = \footnotesize
] {2};
}
info {\draw (visualization cs:x = 1,
y = {(1 / .5 ^ 1.4)}
) circle [radius = 1pt]
node [above,
font = \footnotesize
] {3};
}
info {\draw (visualization cs:x = 2,
y = {(1 / 1.5 ^ 1.4)}
) circle [radius = 1pt]
node [right,
font = \footnotesize
] {4};
};
\end{tikzpicture}
\end{document}
但两种情况下的结果是一样的：
我做错了什么？我该怎么做才能做到这一点（箭头指向几乎在两个点之间）：
提前感谢您的帮助和努力！
答案1
这里有一种方法可以将每个数据集一分为二，使它们具有相同的样式，只是其中一个以箭头结尾，而另一个则没有。我不太熟悉这个datavisualization包，但由于它似乎是在绘制函数，所以找到函数上的“中间”点需要找到曲线的弧长，我不确定它是否TikZ具有这样的功能。在我的方法中，您可以看到一些区间在域方面被分成两半，而有些则没有，以使箭头出现在曲线的“中间”。
结果如下：
这是代码（删除了一些空格）：
\documentclass{scrartcl}
\usepackage{tikz}
\usepackage[per-mode = fraction]{siunitx}
\usetikzlibrary{datavisualization.formats.functions,arrows.meta}
\begin{document}
\begin{tikzpicture}[
% Arrow styles for both ends of lines
midarrA/.style={-{Straight Barb[width=4pt,length=4pt,line width=1pt]}},
midarrB/.style={{Straight Barb[width=4pt,length=4pt,line width=1pt]}-}
]
\datavisualization[
scientific axes = {clean,end labels},
x axis = {label = $\frac{v}{\si{\cubic\m\per\kg}}$},
y axis = {label = $\frac{p}{\si{\bar}}$},
data/format = function,
% Two parts for each data set
visualize as smooth line/.list = {
isentropic_press 1, isentropic_press 2,
isobaric 1, isobaric 2,
isentropic_decompress 1, isentropic_decompress 2
},
style sheet = vary dashing,
% Manually set pairs of data sets to have the same style
/data point/set/isentropic_press 1/.initial=1,
/data point/set/isentropic_press 2/.initial=1,
/data point/set/isobaric 1/.initial=2,
/data point/set/isobaric 2/.initial=2,
/data point/set/isentropic_decompress 1/.initial=3,
/data point/set/isentropic_decompress 2/.initial=3,
% Manually choose which part has the arrow at the end or beginning
isentropic_press 1 = {label in legend = {text = isentrope Verdichtung}},
isentropic_press 2 = {style={midarrB}},
isobaric 1 = {style={midarrA}},
isobaric 2 = {label in legend = {text = isobare Abkühlung}},
isentropic_decompress 1 = {style={midarrA}},
isentropic_decompress 2 = {label in legend = {text = isentrope Entspannung}}
]
% Split intervals of data sets as appropriate
data[set = isentropic_press 1] {var x : interval[.5:1]; func y = 1 / \value x ^ 1.4;}
data[set = isentropic_press 2] {var x : interval[1:2]; func y = 1 / \value x ^ 1.4;}
data[set = isobaric 1] {var x : interval[.5:.75]; func y = 1 / .5 ^ 1.4;}
data[set = isobaric 2] {var x : interval[.75:1]; func y = 1 / .5 ^ 1.4;}
data[set = isentropic_decompress 1] {var x : interval[1:1.35]; func y = 1 / (\value x - .5) ^ 1.4;}
data[set = isentropic_decompress 2] {var x : interval[1.35:2]; func y = 1 / (\value x - .5) ^ 1.4;}
% Accent important points
info {\draw (visualization cs:x = 2, y = {(1 / 2 ^ 1.4)}) circle [radius = 1pt] node [right, font = \footnotesize] {1};}
info {\draw (visualization cs:x = .5, y = {(1 / .5 ^ 1.4)}) circle [radius = 1pt] node [above, font = \footnotesize] {2};}
info {\draw (visualization cs:x = 1, y = {(1 / .5 ^ 1.4)}) circle [radius = 1pt] node [above, font = \footnotesize] {3};}
info {\draw (visualization cs:x = 2, y = {(1 / 1.5 ^ 1.4)}) circle [radius = 1pt] node [right, font = \footnotesize] {4};};
\end{tikzpicture}
\end{document}
也许比我更聪明的人可以将其做成宏。
答案2
我尝试过，但很遗憾未能让你的示例以期望的方式协作。解决方案pgfplots对你有用吗？
结果：
\documentclass[margin=2mm,tikz]{standalone}
\usepackage{pgfplots}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usetikzlibrary{decorations.markings}
\usepackage[per-mode = fraction]{siunitx}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
cycle list name=linestyles,
legend style={
cells={anchor=east},
legend pos=outer north east,
},
xlabel = {$\frac{v}{\si{\cubic\m\per\kg}}$},
ylabel = {$\frac{p}{\si{\bar}}$},
xlabel style = {at={(axis description cs:1.1,0.2)}},
ylabel style = {at={(axis description cs:0.1,1.1)},rotate=-90},
]
\addplot+[
domain=2:0.5,
decoration={
markings,
mark=at position 0.5 with {\arrow [scale=1.5]{stealth}}},
postaction={decorate},
] {1/(x^1.4)};
\addplot+[
domain=0.5:1,
decoration={
markings,
mark=at position 0.5 with {\arrow [scale=1.5]{stealth}}},
%postaction={nomorepostaction,decorate},
postaction={decorate},
] {1/(0.5^1.4)};
\addplot+[
domain=1:2,
decoration={
markings,
mark=at position 0.5 with {\arrow [scale=1.5]{stealth}}},
postaction={decorate},
] {1/((x-0.5)^1.4)};
\draw (axis cs:2,1/2^1.4) circle (1pt) node[right,font=\footnotesize] {1};
\draw (axis cs:0.5,1/0.5^1.4) circle (1pt) node[above,font=\footnotesize] {2};
\draw (axis cs:1.0,1/0.5^1.4) circle (1pt) node[above,font=\footnotesize] {3};
\draw (axis cs:2,1/1.5^1.4) circle (1pt) node[right,font=\footnotesize] {4};
\legend{isentrope Verdichtung,isobare Abkühlung,isentrope Entspannung}
\end{axis}
\end{tikzpicture}
\end{document}