# Draw two circles with line connecting them as in attachment

O-->--O

Sorry I could not post the image.

Edit* Thank you so much.

Can you help me more? Here is my code. I need to draw that mid-arrowed line between the dot-filled circles.

Thank you

\begin{tikzpicture}
\draw [dotted] (0,1) -- (0,10);
\draw [dotted] (1.5,1.3) -- (1.5,10);
\draw [dotted] (3.0,1.3) -- (3.0,10);
\draw [dotted] (4.5,1.3) -- (4.5,10);
\draw [dotted] (6.0,1.3) -- (6.0,10);
\draw [dotted] (7.5,1.3) -- (7.5,10);

% Lower Row
\filldraw[pattern=dots] (7.5,1) circle (0.2) ;
\filldraw[pattern=dots] (6.0,1) circle (0.2);
\filldraw[pattern=dots] (4.5,1) circle (0.2);
\draw (3.0,1) circle (0.2);
\end{tikzpicture}

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Can you post a link to an image showing what you need? A user with sufficient privileges will edit your question and insert it then. Plus it would be nice to post your code so far. –  Count Zero Dec 18 '12 at 11:15
Does TikZ: How to draw an arrow in the middle of the line? or TikZ-pgf directed graph: change arrow color and location help you in finding a solution for the arrow? How are the circles specified? The arrows library gives you o-o. –  Qrrbrbirlbel Dec 18 '12 at 11:36

Here is a modification of your posted code with the arrows added.

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{patterns,calc}

\begin{document}
\begin{tikzpicture}
\draw [dotted] (0,1) -- (0,10);
\draw [dotted] (1.5,1.3) -- (1.5,10);
\draw [dotted] (3.0,1.3) -- (3.0,10);
\draw [dotted] (4.5,1.3) -- (4.5,10);
\draw [dotted] (6.0,1.3) -- (6.0,10);
\draw [dotted] (7.5,1.3) -- (7.5,10);

% Lower Row
\draw[pattern=dots] (7.5,1) node[circle,minimum size=0.4cm,draw,fill] (A) {};
\draw[pattern=dots] (6.0,1) node[circle,minimum size=0.4cm,draw,fill] (B) {};
\draw[pattern=dots] (4.5,1) node[circle,minimum size=0.4cm,draw,fill] (C) {};
\draw (3.0,1) circle (0.2);

% Arrows
\draw[->] (B.east) -- ($(B.east)!0.5!(A.west)$);
\draw ($(B.east)!0.5!(A.west)$) -- (A.west);
\draw[->] (C.east) -- ($(C.east)!0.5!(B.west)$);
\draw ($(C.east)!0.5!(B.west)$) -- (B.west);
\end{tikzpicture}

\end{document}


The main change is to turn the circles in to nodes that are labelled. We can then refer to anchor positions such as A.west for attaching the lines.

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Something like this?

\input tikz
\usetikzlibrary{decorations.markings}
\tikzset{circ/.style={circle, draw, fill=white},
conn/.style={postaction=decorate, decoration={
markings, mark=at position .55 with {\arrow{stealth}}}}}

\tikz\draw[conn] (0,0) node[circ]{} -- +(1,0) node[circ]{};
\bye


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the description in the question sounds to me like a dynkin diagram. if that's the case, the circles here are much larger than the usual in such diagrams, and/or the arrowhead much smaller. –  barbara beeton Dec 18 '12 at 14:05
@barbara: Yes, then it is more difficult (not the size of the circles; that could just be a, say, inner sep=.75ex, but all the other dynkin diagram reqs, like double lines with large angle arrows etc.) –  morbusg Dec 20 '12 at 6:50