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Re: fast summing alternative?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg128369] Re: fast summing alternative?
  • From: Ray Koopman <koopman at sfu.ca>
  • Date: Wed, 10 Oct 2012 01:26:13 -0400 (EDT)
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On Oct 8, 9:48 pm, Ray Koopman <koop... at sfu.ca> wrote:
> 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 ]

This should be faster:

tab3 = Transpose[ MapThread[Dot,{weights,#}]& /@ Partition[
       UnitStep[Plus@@Transpose@Tuples@{sortMat,-newMat}], bNum] ]



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