How can I draw an area under a thermodynamic graph?

Question

My MWE:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings, arrows, arrows.meta,patterns.meta}
\tikzset{
    midar/.style 2 args={
        very thick,
        decoration={name=markings,
            mark=at position .55 with {\arrow{latex}},
            mark=at position 0 with {\fill circle (2pt);},
            mark=at position 1 with {\fill circle (2pt);}}
        ,postaction=decorate,
    },
}
\begin{document}
\begin{tikzpicture}[thick]
    \draw[-{Latex}] (0,0) -- (0,5) node[above] {$P$};
    \draw[-{Latex}] (0,0) -- (5,0) node[right] {$V$};

    \draw[dashed] (0,4) node[left] {$P_{1}$} -| (1,0) node[below] {$V_{1}$};
    \draw[dashed] (0,1) node[left] {$P_{2}$} -| (4,0) node[below] {$V_{2}$};

    \draw (1,4) node[above left]{1};   
    \draw (4,1) node[above right]{2};  
    \draw[midar] (1,4) arc (180:270:3 and 3);
\end{tikzpicture}


\end{document}

This is the picture that I get from the code:

This is an idea for what I'm trying to do:

In addition to providing us with code fragments in your question, consider also submitting the complete code that can be compiled to produce the shown output. The complete code is also called as Minimal Working Example (MWE). So we don't need to reassemble your code fragments. — Display Name, May 05 '21 at 23:50

Ukiyo-E · Accepted Answer · 2021-05-05T23:53:29.810

12

Append the following code at the end of the tikzpicture environment

\fill[pattern=north east lines, pattern color=red] (4,0) -- (1,0) -- (1,4) arc (180:270:3 and 3) -- cycle;

Of course, you need to add \usetikzlibrary{patterns} in your preamble.

edited May 05 '21 at 23:53

answered May 05 '21 at 23:45

Ukiyo-E

728

Thank you, It worked! – Mario Tafur May 05 '21 at 23:52

Roland · Answer 2 · 2021-05-06T07:30:05.260

Another possibility if you know the function of your plot you can use fillbetween:

\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\usetikzlibrary{arrows.meta,patterns}
\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    xlabel={V},
    ylabel={P},
    yticklabels={,,},
    ytick style={draw=none},
    xticklabels={,,},
    xtick style={draw=none},
    samples=200,
    axis lines=center,
    ymin=0,xmin=0,
    ymax=10,xmax=10,
    no marks,
    every axis x label/.style={
        at={(ticklabel* cs:1.05)},
        anchor=west,
    },
    every axis y label/.style={
        at={(ticklabel* cs:1.05)},
        anchor=south,
    },
    ]
    \addplot[blue,domain=2:4,name path=A] {15e^(-0.4x)+2}; %plot
    \addplot[blue,domain=2:3,-Stealth] {15e^(-0.4x)+2}; %arrow plot
    \addplot+[black,domain=2:4,name path=B] {0};     % dummy plot
    \addplot+[pattern=north east lines,pattern color=red!60!white] fill between[of=A and B,soft clip={domain=2:4}]; % fillingbetween A and B
\addplot+[dashed,black,domain=0:2] {8.74};
\addplot+[dashed,black,domain=0:4] {5.03};
\addplot+[black,ycomb] coordinates {(2, 8.74)};
\addplot+[black,ycomb] coordinates {(4, 5.03)};

\coordinate (m1) at (axis cs:2,8.74); %mark1
\coordinate (m2) at (axis cs:4,5.03); %mark2



\end{axis}
\filldraw[fill=blue,draw=blue] (m1) circle(0.05) node[above] {\small 1};
\filldraw[fill=blue,draw=blue] (m2) circle(0.05) node[right] {\small 2};



\end{tikzpicture}
\end{document}

Disclaimer: I only upvote correct answers accompanied with complete code. — Display Name, May 06 '21 at 02:51

Zarko · Answer 3 · 2021-05-06T07:06:24.320

5

Edit: corrected function domain, added declared function f(x) and added missed elements of diagram.

A variation of @Roland answer with use of the patterns.meta library and a wee bit shorter code:

\documentclass[border=3.141592]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.17}
\usepgfplotslibrary{fillbetween}
\usetikzlibrary{arrows.meta,
                decorations.markings,
                patterns.meta}
\begin{document}
    \begin{tikzpicture}[
->-/.style = {decoration={%
    name=markings,
         mark=at position 0.5 with {\arrow{Stealth}}},
    postaction=decorate},
dot/.style = {circle, fill=blue, inner sep=0pt, minimum size=4pt,
              node contents={}},
                        ]
\begin{axis}[
declare function = {f(\x)=(12e^(-1.4\x)+1);},

    axis lines=middle,
    xlabel=$V$, x label style={anchor=west},
    ylabel=$P$, y label style={anchor=south},
    xtick=\empty,
    ytick=\empty,
    xmin=0, xmax=5,
    ymin=0, ymax=5,
    clip=false,
    domain=1:4,
    every axis plot post/.append style={very thick, blue}
    ]
\addplot [name path=A] {f(x)}; %plot
\addplot [draw=none, name path=B] {0}; % x-domain
\addplot +[pattern={Lines[angle=45,distance={3pt}, line width=0.2pt]},
           pattern color=red] 
        fill between[of=A and B]; % patterns
\addplot [->-] {f(x)}; % for arrow on the middle of curve
%
\draw[densely dashed] (0,{f(1)}) node[left] {$P_1$} 
        -| (1,0) node[below] {$V_1$}    node[pos=0.5,dot,dot,label=1];
\draw[densely dashed] (0,{f(4)}) node[left] {$P_2$} 
        -| (4,0) node[below] {$V_2$}    node[pos=0.5,dot,dot,label=2];
\end{axis}
    \end{tikzpicture}
\end{document}

edited May 06 '21 at 07:06

answered May 06 '21 at 02:38

Zarko

296,517

Disclaimer: I only upvote correct answers accompanied with complete code. – Display Name May 06 '21 at 02:51
1

@Kim : Good to know! ;-) – AlexG May 06 '21 at 07:09
@AlexG: Double upvotes for answers with animate. :-) – Display Name May 06 '21 at 07:30
@Kim : I knew you would have multiple accounts :-D – AlexG May 06 '21 at 07:35
@AlexG: Considering your expertise, I believe you can create a special PSTricks package for drawing stereometry as what I asked in this question. :-) – Display Name May 06 '21 at 07:41
@Kim : Oh my, you are by far overrating my skills... The mostly french-speaking PSTricks Guru(s) publish elsewhere: http://pstricks.blogspot.com – AlexG May 06 '21 at 07:55
@AlexG: No. I am not overrating but telling a truth. I know that site, but I cannot understand his explanation in French. – Display Name May 06 '21 at 08:05

How can I draw an area under a thermodynamic graph?

3 Answers3