Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Software » comp.soft-sys.math.mathematica

Topic: [mg23007] Chop? Programming Challenge!!
Replies: 1   Last Post: Apr 15, 2000 3:43 AM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View  
Russell Towle

Posts: 70
Registered: 12/3/04
RE: [mg23007] Chop? Programming Challenge!!
Posted: Apr 15, 2000 3:43 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

Hi David,

I'm afraid I was a little premature in my celebration of a new vector union
function. I tried it in my notebook which takes solid sections of
four-dimensional polytopes. When the polytopes are convex I use a
ConvexHull function to make the sections in the 3-space. This function is
sensitive to duplicate points, so I always run the points of the section
through vunion before passing them to ConvexHull3D.

In my test, most point-sets worked fine, but in one case, out of 20, the
new function returned 81 points, the old, 80. And there were only 80
distinct points.

I was curious to see how the new function would work on the 4-vectors
themselves, before projecting into the 3-space. Here too my vunion function
returned a list of 80 distinct 4-vectors. But the new function returned a
list of 92. So it failed badly with the 4-vectors.

I suspect the problem is the same as before: the ordering of the vectors.
In the spurious list of 81 3-vectors, the two duplicates were separated by
half-dozen other vectors, and neither contained a 0.

It seems that we must discover an iron-clad way to order a Chopped list of
n-vectors.

Thanks again!

Russell Towle
Box 141
Dutch Flat, CA 95714
(530) 389-2872







Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.