> On Oct 18, 2015, at 9:14 AM, xxxxxx@shadowgard.com wrote:
>
> I need an equation I can easily plug into a BASIC program. I need to
> draw several sizes of ellipse, all with the same focal points but
> different major axis sizes.
>
> Call the distance bettween the foci D.
>
> So the foci would be on the X-axis at -0.5D and +0.5D. And the major
> axis would be expressed in terms of D.
>
> I'm sure there's some simple way to work this, but I haven't had any
> luck finding it.
>
> Basicly, I'm trying to set something up that has effects based on the
> sum of the "emissions" from the focal points (thus having an
> elliptical area of effect).
>
> But I need to make some of it work with other things, so I need to
> try different values of D & the major axis to get things to both
> "look right" and figure clearances for other stuff.

Here’s the basic equation for an ellipse : <http://www.mathwarehouse.com/ellipse/equation-of-ellipse.php>, but this looks more easily translatable to a program to do what you want: <https://en.wikipedia.org/wiki/File:Ellipse_Properties_of_Directrix_and_String_Construction.svg>

--
Bruce Johnson
University of Arizona
College of Pharmacy
Information Technology Group

Institutions do not have opinions, merely customs