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MathGroup Archive 2006

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Re: distance function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70138] Re: distance function
  • From: Peter Pein <petsie at dordos.net>
  • Date: Thu, 5 Oct 2006 03:32:36 -0400 (EDT)
  • References: <200609300912.FAA13156@smc.vnet.net> <efq5f5$28g$1@smc.vnet.net>

Chris Chiasson schrieb:
> Could someone please explain why Mathematica seems to be expecting the
> output of cc to be a vector?
> 
> pts[1]=Table[{Random[],Random[]},{3}];
> cc[p_,p_]=0;
> cc[p_,q_]:=cc[q,p]=Sqrt[#.#]&[p-q];
> ccC=Compile[{{p,_Real,1},{q,_Real,1}},cc[p,q]];
> Outer[ccC,pts[1],pts[1],1]
> 

I guess it's because p and q are vectors and compile doesn't analyze cc.

b.t.w. It doesn't make much sense to compile only the call to a function 
but not the function itself:

pts[1] = Table[Random[], {1000}, {2}];
ccC = Compile[{{p, _Real, 1}, {q, _Real, 1}}, cc[p, q], {{_cc, _Real}}];
Timing[Outer[ccC, pts[1], pts[1], 1];]

lasts 17.5 seconds but if you compile cc inline:

pts[1] = Table[Random[], {1000}, {2}];
ccC = Compile[{{p, _Real, 1}, {q, _Real, 1}}, Evaluate@cc[p, q]];
Timing[Outer[ccC, pts[1], pts[1], 1];]

only 1.8 seconds are necessary.

Peter


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