How to draw an ellipse?

Question

As I know, I can draw a circle using:

\draw (1,0) circle (2)

I try this kind of method to draw a \draw ellipse, failed. Would you tell me how to draw a ellipse? What's wrong with the code below?

The code is:

\documentclass{minimal}

\usepackage{tikz}
\usepackage{verbatim}
\begin{document}

% Define the rings. Store them in macros to make things
% more flexible.
 \def\boundellipse {(0,0) ellipse (10,5)}

\begin{tikzpicture}
    % Then we draw the rings
\draw \boundellipse;

\end{tikzpicture}

\end{document} 

Answer 1

PSTricks' ellipse syntax might be closer to your requirement. Here it is \psellipse(<centerX, centerY>)(<semi-major-length, semi-minor-length>).

\documentclass[pstricks,border=12pt]{standalone}

\begin{document}
\begin{pspicture}[showgrid=true](8,6)
    \psellipse[linecolor=red](4,3)(4,3)
    \pscircle[linecolor=blue](4,3){2}
\end{pspicture}
\end{document}

Answer 2

\documentclass[border=3pt]{standalone}
\usepackage{tikz}

\begin{document}
\tikz \draw (0,0) ellipse (2cm and 1cm);


or

\begin{tikzpicture}
    \draw (0,0) ellipse (2cm and 1cm);
\end{tikzpicture}
\end{document}

EDIT:

\documentclass[border=3pt]{standalone}
\usepackage{tikz}
\def\myellipse{(0,0) ellipse (2cm and 1cm)}


\begin{document}
\tikz \draw \myellipse ;


or

\begin{tikzpicture}
    \draw \myellipse;
\end{tikzpicture}
\end{document}

Answer 3

The pgfmanual gives \draw (a,b) circle [x radius=1cm, y radius=2cm];

With a macro

\newcommand{\boundellipse}[3]% center, x rad, y rad
{(#1) ellipse [x radius=#2,y radius=#3]
}

Answer 4

The notion is xdim and ydim, you are using xdim, ydim:

\documentclass{minimal}
\usepackage{tikz}

\begin{document}

\newcommand{\boundellipse}[3]% center, xdim, ydim
{(#1) ellipse (#2 and #3)
}

\begin{tikzpicture}
\draw \boundellipse{0,0}{10}{5};
\draw \boundellipse{4,1}{-2}{4};
\draw \boundellipse{-2,4}{1}{3};

\end{tikzpicture}

\end{document}

Answer 5

\documentclass{minimal}
    \usepackage{tikz}
        \begin{document} 
    \begin{tikzpicture}[yscale=2]
     \draw (1,0) circle (2);
     \end{tikzpicture}
    \end{document}