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Functional programming puzzle
*To*: mathgroup at christensen.cybernetics.net
*Subject*: [mg1825] Functional programming puzzle
*From*: Count Dracula <lk3a at kelvin.seas.virginia.edu>
*Date*: Thu, 3 Aug 1995 23:52:28 -0400
*Organization*: University of Virginia
In Article: 1079 of comp.soft-sys.math.mathematica
"Wm. Martin McClain" <wmm at chem.wayne.edu> wrote:
> Let ptList = {{1,1,2},{2,1,3},{1,3,2}};
> I want a matrix of distances between the points in ptList.
> Any human would think you could get it with
> Rij[a_,b_]:=Sqrt[(a-b).(a-b)]
> followed by
> Outer[Rij,ptList,ptList]
> But Mathematica returns a mess, because Outer seems
> to Flatten the ptList before running the outer
> product loops.
This will work if you give Outer a Level specification:
dist[x_List] := Sqrt[Map[#1 . #1 & , Outer[Subtract, x, x, 1], {2}]]
ltest = {{1,1,2},{2,1,3},{1,3,2}}
In[4]:= dist[ltest]//MatrixForm
Out[4]//MatrixForm= 0 Sqrt[2] 2
Sqrt[2] 0 Sqrt[6]
2 Sqrt[6] 0
--
Levent Kitis lk3a at cars.mech.virginia.edu lk3a at kelvin.seas.virginia.edu
University of Virginia Department of Mechanical, Aerospace, and Nuclear Engineering
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