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Re: Help with geometry problem required.

  • To: mathgroup at
  • Subject: [mg20829] Re: Help with geometry problem required.
  • From: Michael Ellis <michael at>
  • Date: Wed, 17 Nov 1999 03:40:43 -0500 (EST)
  • Organization: Digital Scientific
  • References: <80nfvr$> <80r01r$>
  • Sender: owner-wri-mathgroup at

Thanks for your help, but when I run this on my PowerMac my MathKernal runs
out of memory (80MB allocated). I am also not sure that Solve doesn't deal
with the extra _List layers since

  {{{x + y}} == {{2}},
    {x - y} == {3}}, {x, y}]
seems to work fine.

Thanks again for your help though.

Jens-Peer Kuska wrote:

> Hi,
> since M.p1==P1 yields Equal[_List,_List] you need Thread[], since there
> is still a list
> of equation lists you must Flatten it:
> Simplify[Solve[
>     Flatten[{Thread[M.p1 == P1], Thread[M.p2 == P2], Thread[M.p3 == P3],
>         DistanceSq[p1, p2] == DistanceSq[P1, P2],
>         DistanceSq[p1, p3] == DistanceSq[P1, P3],
>         DistanceSq[p3, p2] == DistanceSq[P3, P2]}], {a, b, c, d, e, f,
> g, h,
>       i, j, k, l}]]
> will give you the solution you need.
> Hope that helps
>   Jens
> > My Problem:
> > I have three points marked on a piece of rigid card at positions p1, p2
> > and p3. The card is moved, by translation and or rotation, but not
> > otherwise distorted to a new location. The three points p1, p2 and p3
> > are now at new positions say P1, P2 and P3. My question: Is there a 4 by
> > 4 Transform M that uniquely describes this relocation and if so how can
> > I derive M given p1, p2, p3, P1, P2 and P3.

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