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MathGroup Archive 1998

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Re: How to draw an ellipse?



Krishnan Jayakrishnan wrote:
> 
> Does any one know how to construct an ellipse? For example an ellipse
> centered at (0,0) with intercepts at (-a,0,(a,0),(0,-b),(0,b) with
> parametric equation
> x(t) = a*cos(t)
> y(t) = b*sin(t)
> with t increasin from 0 to 2pi radians. --
> Sincerely
> Krishnan Jayakrishnan
> Systems Administrator
> Allied Geophysical Labs
> University of Houston


Several ways:  First, if you just want to display one, then use
Show[Graphics[Circle[{0,0},{a,b}]]].   Of course, you will have to
specify actual numbers for a and b.  Mathematica does not plot in units
of unspecified symbols.

The other way is to use ParametricPlot as in:

ParametricPlot[{2 Sin[t],Cos[t]},{t,0,2 Pi},AspectRatio->Automatic].

You can even use a rectangular plot for the same thing, but you will
have to do two of them: one for positive and negative as in:

Show[Plot[Sqrt[1-x^2],{x,-1,1}],Plot[-Sqrt[1-x^2],{x,-1,1}]]

Based on the way you wrote your equations, you might want to review
section 1.2.5 in the mathematica book on the various kinds of
bracketing.
-- 
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