Re: Equation of a "potato"
- To: mathgroup at smc.vnet.net
- Subject: [mg24532] Re: Equation of a "potato"
- From: "David Bailey" <db at salford-software.com>
- Date: Mon, 24 Jul 2000 03:04:11 -0400 (EDT)
- Organization: University of Salford, Salford, Manchester, UK
- References: <8l0pbk$dqo@smc.vnet.net> <8l3fdk$kvd@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
"Philip C Mendelsohn" <mend0070 at garnet.tc.umn.edu> wrote in message news:8l3fdk$kvd at smc.vnet.net... > Kevin J. McCann (Kevin.McCann at jhuapl.edu) wrote: > : I am doing some illustrations for class notes on vector calculus. I > : would be nice to have some drawings for a "random" 3d shape, i.e. > : something that is fairly rounded and regular like a potato, but not as > : simple as a sphere. Any ideas for the an equation that would draw > : something like this? > > What about making a ParametricPlot of a Sphere where the radius varies > by a small random coefficient? > > I'll see if I can play with this when I get near the computer. > > Phil M > -- > Lottery: a tax on people who are bad at math > There is a trap here. If you plot something like Plot[Sin[t]+Random[],{t,0,2 Pi}] you get a graph which is really just an artifact. The point is that Plot assumes a continuous function and repeatedly divides the interval trying to fit a smooth curve to something that is randomly varying. ParametricPlot3D will behave similarly! I think this will result in a very hairy sphere! I think you could use ParametricPlot3D, but you would have to generate a function r[theta,phi] that was (say) fitted to a number of random values or r for particular theta and phi. This would still suffer from rapid variation near the poles of the sphere. I suspect this problem is a bit more subtle than it looks! David Bailey Salford Software