Labeling Plots?

Question

I haven't been able to find anything on this after searching for a while, so I apologize if this is a duplicate.

I need to replicate the following image:

Here's what I've got so far:

\documentclass{minimal}

%%for graphs
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{pgfplots}
\pgfplotsset{compat=1.10}
\usepgfplotslibrary{fillbetween}
%%end graph code

    \begin{document}
    \begin{tikzpicture}[scale=1]
    \begin{axis}[
            axis x line=bottom,%need to change to bottom to put 0 in 
            axis y line=middle,
            x label style={at={(axis cs: 2.6, -0.12)},anchor=south},%rotate = degrees number can be used to rotate the label
            y label style={at={(axis cs:0, 2.5)},anchor=south},
            xtick={0, 1, 2}, %or {listofvalues, , },
            ytick={0, 1, 2},
            yticklabels={$0$, $1$, $2$},
            xticklabels={$0$, $1$, $2$},
            ymin=0,
            ymax=2.5,
            xmin=0,
            xmax=2.5,
            ylabel=$y$, 
            xlabel=$x$,
            area style,
            ]
        %thick lines
        \draw[draw = black, ultra thick] (axis cs: 0, 0) -- (axis cs: 0, 2);
        \addplot+[draw = black, ultra thick, name path = upper, domain=0:2] {2-x};
        \addplot+[draw = black, ultra thick, name path = lower, domain=0:2] {0};  
        %shading    
        \addplot[gray!40] fill between[of = upper and lower];
    \end{axis}
    \end{tikzpicture}
    \end{document}

It doesn't matter to me where the axis labels are - the main problem is trying to get the x + y = 2 on the line.

How can I get the x + y = 2 on the line?

Answer 1

One way would be to place a node:

\node [rotate=-45, above] at (axis cs: 1,1) {$x + y = 2$};

which requires the use of the axis cs coordinate system and a rotate=.

Alternatively, you can place the node as part of the \addplot using the sloped option:

    \addplot+[draw = black, ultra thick, name path = upper, domain=0:2] {2-x} 
          node [midway, sloped, above, red] {$x + y = 2$};

Notes:

• Please see Why should the minimal class be avoided?

---

Code: Manual Node:

\documentclass{article}
%%for graphs
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{pgfplots}
\pgfplotsset{compat=1.10}
\usepgfplotslibrary{fillbetween}
%%end graph code
\begin{document}
\begin{tikzpicture}[scale=1]
\begin{axis}[
        axis x line=bottom,%need to change to bottom to put 0 in 
        axis y line=middle,
        x label style={at={(axis cs: 2.6, -0.12)},anchor=south},%rotate = degrees number can be used to rotate the label
        y label style={at={(axis cs:0, 2.5)},anchor=south},
        xtick={0, 1, 2}, %or {listofvalues, , },
        ytick={0, 1, 2},
        yticklabels={$0$, $1$, $2$},
        xticklabels={$0$, $1$, $2$},
        ymin=0,
        ymax=2.5,
        xmin=0,
        xmax=2.5,
        ylabel=$y$, 
        xlabel=$x$,
        area style,
        ]
    %thick lines
    \draw[draw = black, ultra thick] (axis cs: 0, 0) -- (axis cs: 0, 2);
    \addplot+[draw = black, ultra thick, name path = upper, domain=0:2] {2-x};
    \addplot+[draw = black, ultra thick, name path = lower, domain=0:2] {0};  
    %shading    
    \addplot[gray!40] fill between[of = upper and lower];
    \node [rotate=-45, above] at (axis cs: 1,1) {$x + y = 2$};
\end{axis}
\end{tikzpicture}
\end{document}

---

Code: Node as part of \addplot:

\documentclass{article}
%%for graphs
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{pgfplots}
\pgfplotsset{compat=1.10}
\usepgfplotslibrary{fillbetween}
%%end graph code
\begin{document}
\begin{tikzpicture}[scale=1]
\begin{axis}[
        axis x line=bottom,%need to change to bottom to put 0 in 
        axis y line=middle,
        x label style={at={(axis cs: 2.6, -0.12)},anchor=south},%rotate = degrees number can be used to rotate the label
        y label style={at={(axis cs:0, 2.5)},anchor=south},
        xtick={0, 1, 2}, %or {listofvalues, , },
        ytick={0, 1, 2},
        yticklabels={$0$, $1$, $2$},
        xticklabels={$0$, $1$, $2$},
        ymin=0,
        ymax=2.5,
        xmin=0,
        xmax=2.5,
        ylabel=$y$, 
        xlabel=$x$,
        area style,
        ]
    %thick lines
    \draw[draw = black, ultra thick] (axis cs: 0, 0) -- (axis cs: 0, 2);
    \addplot+[draw = black, ultra thick, name path = upper, domain=0:2] {2-x} node [midway, sloped, above, red] {$x + y = 2$};
    \addplot+[draw = black, ultra thick, name path = lower, domain=0:2] {0};  
    %shading    
    \addplot[gray!40] fill between[of = upper and lower];
\end{axis}
\end{tikzpicture}
\end{document}