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Re: fast summing alternative?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg128360] Re: fast summing alternative?
  • From: Ray Koopman <koopman at sfu.ca>
  • Date: Tue, 9 Oct 2012 00:40:28 -0400 (EDT)
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  • Delivered-to: l-mathgroup@wolfram.com
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  • References: <k4tth1$sgq$1@smc.vnet.net>

On Oct 7, 11:59 pm, Chris <kristoph.steik... at gmail.com> wrote:
> Dear all
>
> The code below is part of a large compile function I wrote and the inputs, like the matrices weights and newData, are in fact large data files. Thus, I provide them in the following problem as random. Although, written as compile code (with CompilationTarget->"C") it is still too slow for the amounts of data I have to process. I provide two of my fastest alternatives, which sadly are not that fast. I do appreciate any help to make the code faster. Thanks in advance!
>
> (*
> What I do is simple: For each row of newMat and weights I construct a new row. The elements of this new row are the sums of the elements in weights if a certain requirement of the same element in newMat is met.
> *)
>
> Clear[bNum,nNum,weights,newMat,sortMat,tab];
>
> bNum;
> nNum=100;
>
> weights=Table[RandomReal[{-10,10}],{b,1,bNum},{n,1,nNum}];
> newMat=Table[RandomReal[{-10,10}],{b,1,bNum},{n,1,nNum}];
> sortMat=Table[i,{i, -10, 10, 0.1}]; (*elements always evenly spaced*)
>
> (*first alternative*)
> tab=Table[
> Sum[weights[[k,i]]*If[newMat[[k,i]] <= sortMat[[j]],1.,0.],{i,1,nNum}], {k,1,bNum},
> {j,1,Length[sortMat]}];//AbsoluteTiming
>
> (*second alternative*)
> mat=Block[{k=1},
> Reap[Do[
> Sow[Table[Sum[weights[[k,i]]*If[newMat[[k,i]] <= sortMat[[j]],1.,0.],{i,1,nNum}],{j,1,Length[sortMat]}]];
> k++,{bNum}]]][[2,1]];//AbsoluteTiming

tab2 = Transpose @ With[{negnewMat = - newMat}, MapThread[
       Dot, {weights, UnitStep[# + negnewMat]} ]& /@ sortMat ]



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