Drawing circles and arrows using tikz

Question

I am trying to plot two circles one below the other. I also want two draw two arrows (I prefer solid curly arrows) between the circles.

So far I tried the below code, but it is not working. Can anyone help ?

\documentclass[12pt]{beamer}

\usepackage{tikz}
\usepackage{pifont}

\usetikzlibrary{shapes.geometric,arrows}
\tikzstyle{circ} = [circle, minimum size=1cm, text centered, draw = black, fill = red!30]
\tikzstyle{arrow} = [thick,->,>=stealth]

\begin{document}
\begin{frame}{Introduction}
\begin{block}{Model}
\begin{figure}
    \centering
    \begin{tikzpicture}[node distance=1cm]
    \node (env) [circ] {Environment};
    \node (agent) [circ, below of=env] {Agent};
    \draw [arrow] (env) -- (agent);
    \draw [arrow] (agent) -- (env);
    \end{tikzpicture}
\end{figure}
\end{block}
\end{frame}
\end{document}

Answer 1

I guess that you looking for this:

• For above image I employ TikZ library positioning and use its syntax below=of env (observe difference in order of = and of). With this the node distance define distance between nodes borders.

• As you define distance between nodes (without using positioning library), node distance define distance between center of circles. So in your case it should be increased significantly (considering size of nodes' shapes)

• Regarding arrows, for it is used bend left option for edges. If you like to have bend more curved than the picture above shows, than just add angle to bend, for example bend left=45:

• Further costumization of styles I left to you. You can ease to change thickens of arrows and shape borders, their colors, size of text etc.

• Note, use of \tikzstyle{...} = [...] s deprecated. Instead of it is recommended to use \tikzset{ ... } or define styles as options of tikzpicture as is done in MWE below.

\documentclass[12pt]{beamer}

\usepackage{tikz}
\usetikzlibrary{arrows.meta, 
                positioning}
\usepackage{pifont}

\begin{document}
\begin{frame}{Introduction}
\begin{block}{Model}
\begin{figure}
    \centering
    \begin{tikzpicture}[
    node distance = 1cm,
      circ/.style = {circle, draw, fill = red!30,
                     minimum size=1cm, align=center},
every edge/.style = {draw, very thick, -Stealth, bend left}
                        ]
    \node (env)   [circ] {Environment};
    \node (agent) [circ, below=of env] {Agent};
    \draw   (env)   edge[bend left] (agent)
            (agent) edge[bend left] (env);
    \end{tikzpicture}
\end{figure}
\end{block}
\end{frame}
\end{document}