[Tex/LaTex] How to draw direction arrows in lines and arcs

tikz-pgf

I want to draw the following picture. And so far my code is the following:

\begin{tikzpicture}[xscale=1.5,yscale=1.5]
\draw [->] (0,-2) --(0,2) node [left] {${\rm Im}(p)$};
\draw [->] (-2,0) --  (2,0) node [below] {${\rm Re}(p)$};
\draw [thick] (1,-1.8) --(1,1.8);
\draw [fill] (0,-1.8) --(1,-1.8); \draw [fill] (0,1.8) --(1,1.8);
\draw [black] (0,1.8) arc [radius=1.8, start angle=90, end angle = 270];
\draw [fill] (0.5,1) circle [radius=.05];
\draw [fill] (0.5,0.5) circle [radius=.05];
\draw [fill] (0.5,-0.5) circle [radius=.05];
\draw [fill] (0.5,-1) circle [radius=.05];
\node at (1.15,-0.15) [] {$\sigma$};
\draw [fill] [<-] (0.65,1.1)--(1.5,1.5);
\end{tikzpicture}

I would appreciate if anyone could help me draw the direction arrows and is it possible to include text in the graph?

Thank you in advance for your help.

Best Answer

\documentclass[tikz, border=3mm]{standalone}
\usetikzlibrary{decorations.markings}

\begin{document}

\begin{tikzpicture}[scale=0.5,
decoration = {markings,
    mark=at position 0.10 with {\arrow {latex}},
    mark=at position 0.35 with {\arrow {latex}},
    mark=at position 0.70 with {\arrow {latex}},
    mark=at position 0.90 with {\arrow {latex}}
              }
                    ]
% axes
\draw [->] (0,-3.3) -- (0,4) node [left]  {${\rm Im}(p)$};
\draw [->] (-3.3,0) -- (4,0) node [below] {${\rm Re}(p)$};
% poles
    \foreach \i in {-2,-1, 1, 2}{\node at (1,\i) {$\times$};}
% curve
\draw[postaction={decorate},thick]
        (2,0) node[below right] {$\sigma$}
              |- (0,3) arc (90:270:3) -| (2,0);
\draw[<-,shorten <=2mm] (1,2)-- ++ (30:1.5) node[right] {poles};
\end{tikzpicture}
\end{document}

gives

Arrows on curve around s-plane are determined by decorations.markings TikZ library.

Related Solutions

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

A solution which allows to draw intersection segments of any two intersections is available as tikz library fillbetween.

This library works as general purpose tikz library, but it is shipped with pgfplots and you need to load pgfplots in order to make it work:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}];

\end{tikzpicture}

\end{document}

enter image description here

The key intersection segments is described in all detail in the pgfplots reference manual section "5.6.6 Intersection Segment Recombination"; the key idea in this case is to

create a temporary path temp1 which is the first intersection segment of red and blue, more precisely, it is the first intersection segment in the Left argument in red and blue : red. This path is drawn as thin black path. Substitute its \draw statement by \path to make it invisible.
Compute the desired intersection segment by intersecting temp1 and green and use the correct intersection segment. By trial and error I figured that it is the third segment of path temp1 which is written as L3 (L = left argument in temp1 and green and 3 means third segment of that path).

The argument involves some trial and error because fillbetween is unaware of the fact that end and startpoint are connected -- and we as end users do not see start and end point.

Note that you can connect these path segments with other paths. If such an intersection segment should be the continuation of another path, use -- as before the first argument in sequence. This allows to fill paths segments:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,fill=blue,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}]  
    [intersection segments={of=temp1 and green, sequence={--R2}}]
;

\end{tikzpicture}

\end{document}

enter image description here

How to change the radius of circle in a node in tikz style

First, don't use tikzstyle which is deprecated, but use tikzset instead. Then, define your nodes as circle with inner sep=0pt (you can also set the outer sep to 0pt), and with a minimum width which is your node diameter.

Finally, you can make other node style inherit a previous one like I did. The selected vertex inherits all parameters from the vertex style, and you can add/replace some afterwards (like the filling here).

\documentclass[]{beamer}
\usetheme{Darmstadt}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
    \begin{frame}{}
        \begin{tikzpicture}[>=latex]
        \tikzset
            {
            vertex/.style={circle, inner sep=0pt, outer sep=0pt, minimum width=1cm,fill=black!10},
            selected vertex/.style = {vertex, fill=red!30},
            nedge/.style = {-}
            }

        \node[vertex] (v1) at (3,0) {v1};
        \node[vertex] (v2) at (0,-1) {v2};
        \node[vertex] (v3) at (6,-1) {v3};
        \draw[nedge] (v1) -- (v2);
        \draw[nedge] (v1) -- (v3);
    \end{tikzpicture}
\end{frame}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

How to change the radius of circle in a node in tikz style

Related Question