Swoopy things

Got distracted from writing by downloading GraphCalc. Big mistake. Although I only did math up to the beginning calculus sequence in uni, I'm somewhat fascinated by it, and I like trying to figure out how to graph/if I can graph a certain shape.

Which led to looking up all kinds of silly things on Wikipedia and MathWorld, like how to draw ellipses (I forgot *paiseh paiseh*).

Found out what spline curves are at last. So when you drag the little handle things around in Paint Shop, the angle of the handle is the first derivative and the length of the handle is the...second derivative? I still haven't dared to try much with the vector graphics.

I think the only way to draw a closed curve in GraphCalc is to make one function for the top half and one function for the bottom half...and you still get holes around the equator where the slope is infinite. Otherwise it's very cool. I used GraphCalc a long time ago to draw slices through a 3D (top half sphere, bottom half paraboloid) to make a collapsible egg of thin card as a gift for a friend.

I suppose if you wanted to (and knew a lot about engineering) you could make a really big paraboloid, cover it in tinfoil, and have your own solar oven. Or Astro dish.