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MathGroup Archive 1996

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Re: programming competition Correction

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4951] Re: [mg4904] programming competition Correction
  • From: Allan Hayes <hay at haystack>
  • Date: Mon, 7 Oct 1996 02:02:17 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Please change line 6 in the code that I gave from
	If[n<2, {#1},
to      If[n<1, {#1},

giving

linearInterpolate2[ li_List, m_ ] :=
   Block[{},
      Append[
         Join@@Partition[ li, 2,1,
	    (  n=Floor[Sqrt[(#2-#1).(#2-#1)//N]/m];
	       If[n<1,
	       {#1},
		    Table[#1 + k #2, {k,0,n}]&[#1,(#2-#1)/(n+1)],
		
	       ]
	    )&
	  ],
	  Last[li]
      ]
   ];

(the error crept in because of changing from Ceiling to Floor)

I time it (and check it!) against the fastest code in  Xah Lee's  
posting "[mg4900] Re: programming competition",  due to  
espen.haslund at fys.uio.no (Espen Haslund):

linearInterpolateEH2[ li_List, maxLength_ ]:=
Module[{p1, p2, n},
 Append[Join @@ Table[{p1, p2} = li[[{i, i+1}]];
  n = Max[Ceiling[Sqrt[#.#]&[N[p2-p1]]/maxLength],1];
   Table[p1+(p2-p1)j,{j,0,1-.5/n,1./n}],
    {i,1,Length[li]-1}], Last[li] ]
]


li = Table[{Random[], Random[]}, {1000}];
maxLength = .1;

a4 = Timing@ linearInterpolateEH2[ li, maxLength];
a5 = Timing@ linearInterpolate2[ li, maxLength];

First /@ {a4,a5}

SameQ@@ Last /@ SetPrecision[{a4,a5},5]

{21.3 Second, 14.8333 Second}

True

Allan Hayes
hay at haystack.demon.co.uk
URL:haystack.demon.co.uk

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