A question on feasible region

Question

I faced a difficulty to name the corner point of the feasible region determined by the below LaTeX/TikZ code, who can help me.

\begin{figure}[htpb]
\centering
\begin{tikzpicture}

    \draw[gray!50, thin, step=0.5] (-2,-2) grid (14,14);
    \draw[very thick,->] (-2,0) -- (14,0) node[right] {$x$};
    \draw[very thick,->] (0,-2) -- (0,14) node[above] {$y$};

   \foreach \x in {-2,...,14} \draw (\x,0.5) -- (\x,-0.5) node[below] {\tiny\x};
   \foreach \y in {-2,...,14} \draw (-0.5,\y) -- (0.5,\y) node[right] {\tiny\y};

    \fill[blue!50!cyan,opacity=0.3] (0,0)-- (0,5) -- (6,11) -- (8,10) --(13,0) --cycle;
\put(0,0){A}\put(0,5){B}\put(6,11){C}\put(8,10){D}\put(13,0){E}
    \draw (-2,3) -- node[above,sloped] {\tiny$-x+y\leq5$} (9,14);
    \draw (6,14) -- node[above,sloped] {\tiny$2x+y\leq26$} (14,-2);
    \draw (0,14) -- node[above right,sloped] {\tiny$2x+4y\leq56$} (14,7);

\end{tikzpicture} 
\caption{Feasible Region of the problem}
\label{fig:ch3:c2}
\end{figure}

Are you trying to mix xypic or PSTricks or picture mode with TikZ syntax? \put commands should not be there. — percusse, Feb 27 '13 at 16:16
I want to give name for each corner points. I tried to use for instance \put (0,0){A}\put (0,5){B} \put(6,11){C} \put(8,10){D} \put(13,0){E}, but it doesn't work. — gtolessa, Feb 27 '13 at 16:21
Welcome to TeX.sx! No need to add thanks, simply upvote any good replies you may receive. It is our preferred way to show appraciation, it makes posts more concise. — Peter Jansson, Feb 27 '13 at 16:30
You have used the [tag:pgfplots] tag. The code you provided only shows TikZ. Are you also looking for a pgfplots solution? — Qrrbrbirlbel, Feb 27 '13 at 16:50

Qrrbrbirlbel · Answer 1 · 2013-02-27T16:55:24.763

As percusse said in his comment: \put has nothing to do in a TikZ picture.

You probably want to use \node (with text) or \coordinate (saves the coordinate under a name). I used a combination of both (and a loop to save TikZ macros and my mind).

First the actual points are saved under a name (A, B, …):

\coordinate (<name>) at (<x>, <y>);

and with the help of the label option a node is added so that a reader can identify the points by their name. Instead of the label option, I could have used a \node which adds the text.

\foreach \x/\y/\t/\p in {0/0/A/below left,
                         0/5/B/above left,
                         6/11/C/above,
                         8/10/D/below left,
                         13/0/E/above right}{% as two commands are used, those need to be
                                             % enclosed in { } so that they both are looped.
  \coordinate (\t) at (\x,\y);
  \node[\p] at (\t) {\t};
}

In the \fill command I have used the stored coordinate names.

In the second example I have used the the intersections library to let TikZ find the right points. You can now change the lines and TikZ does the rest for you.

Code

\documentclass[tikz]{standalone}
\usetikzlibrary{intersections}
\begin{document}
\begin{tikzpicture}
  \draw[gray!50, thin, step=0.5] (-2,-2) grid (14,14);
  \draw[very thick,->] (-2,0) -- (14,0) node[right] {$x$};
  \draw[very thick,->] (0,-2) -- (0,14) node[above] {$y$};

 \foreach \x in {-2,...,14} \draw (\x,0.5) -- (\x,-0.5) node[below] {\tiny\x};
 \foreach \y in {-2,...,14} \draw (-0.5,\y) -- (0.5,\y) node[right] {\tiny\y};

  \foreach \x/\y/\t/\p in {0/0/A/below left,
                           0/5/B/above left,
                           6/11/C/above,
                           8/10/D/below left,
                           13/0/E/above right}
    \coordinate[label={\p:\t}] (\t) at (\x,\y);
  \fill[blue!50!cyan,opacity=0.3] (A) -- (B) -- (C) -- (D) -- (E) -- cycle;

  \draw (-2,3) -- node[above,sloped]       {\tiny$-x+y\leq5$}   (9,14);
  \draw (6,14) -- node[above,sloped]       {\tiny$2x+y\leq26$} (14,-2);
  \draw (0,14) -- node[above right,sloped] {\tiny$2x+4y\leq56$} (14,7);
\end{tikzpicture} 

\begin{tikzpicture}
  \draw[gray!50, thin, step=0.5] (-2,-2) grid (14,14);
  \draw[very thick,->, name path=x axis] (-2,0) -- (14,0) node[right] {$x$};
  \draw[very thick,->, name path=y axis] (0,-2) -- (0,14) node[above] {$y$};

  \foreach \x in {-2,...,14} \draw (\x,0.5) -- (\x,-0.5) node[below] {\tiny\x};
  \foreach \y in {-2,...,14} \draw (-0.5,\y) -- (0.5,\y) node[right] {\tiny\y};

  \draw[name path=line 1] (-2,3) -- node[above,sloped]       {\tiny$-x+y\leq5$}   (9,14);
  \draw[name path=line 2] (6,14) -- node[above,sloped]       {\tiny$2x+y\leq26$} (14,-2);
  \draw[name path=line 3] (0,14) -- node[above right,sloped] {\tiny$2x+4y\leq56$} (14,7);

  \tikzset{
    name intersections={of=y axis and x axis, name=A},
    name intersections={of=y axis and line 1, name=B},
    name intersections={of=line 1 and line 3, name=C},
    name intersections={of=line 3 and line 2, name=D},
    name intersections={of=x axis and line 3, name=E},
  }
  \foreach \t/\p in {A/below left,
                     B/above left,
                     C/above,
                     D/below left,
                     E/above right}
     \node[fill,circle,minimum size=6\pgflinewidth,inner sep=0pt,label={\p:\t}] at (\t) {};
  \fill[blue!50!cyan,opacity=0.3] (A) -- (B) -- (C) -- (D) -- (E) -- cycle;
\end{tikzpicture} 
\end{document}

Output

enter image description here

A question on feasible region

1 Answers1

Code

Output