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.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com