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how can i covert following variables as Indexed variables ?

Asked by Raihan Ul Islam on 6 Sep 2019
Latest activity Commented on by Raihan Ul Islam on 8 Sep 2019
I have following function. I want to improve the execution time. Matlab profiler is showing following messgae. How can i convert 'input' and 'transformedRefVal1Rt' as indexed variables.
If 'input' is an indexed variable, performance can be improved using logical indexing instead of FIND.
If 'transformedRefVal1Rt' is an indexed variable, performance can be improved using logical indexing instead of FIND.
Here Input is 1x49457 and RtRef is 1x3 Matrix. I am also attaching the data of input,RtRef,numberOfInputData
function transformedRefVal1Rt=inputTransformGPU(input,RtRef,numberOfInputData)
[M,N]=size(RtRef);
transformedRefVal1Rt=gpuArray(zeros(numberOfInputData,N));
input(find(input>RtRef(1)))=RtRef(1);
input(find(input<RtRef(N)))=RtRef(N);
for j=1:N
transformedRefVal1Rt(find(input== RtRef(j)),j)=1;
end
for j=1:N-1
aa=find((RtRef(j)> input ) & (input>RtRef(j+1)));
transformedRefVal1Rt(aa,j+1)=(RtRef(j)-input(aa))/(RtRef(1)-RtRef(j+1));
transformedRefVal1Rt(aa,j)=1-transformedRefVal1Rt(aa,j+1);
end
end

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1 Answer

Answer by Rik
on 6 Sep 2019
 Accepted Answer

No need for a conversion, they already are indexed variables. Lets give a small example of what this message means:
data=1:5;
L= data<2.5; %generate logical array [true true false false false]
ind=find(L); %generate linear index [1 2]
data(ind) %returns [1 2]
data(L) %returns [1 2]
Because you skip a function call if you directly use the logical array to index you get a performance gain.
In your case you can simply remove the find calls, even without needing to edit any other part of your code.

  5 Comments

Thanks for your comments. it will be very nice if you could give some example of array operation. The N value will not go above 4.
With such a low loop count I doubt you will see much gain in vectorizing this code. I also don't really see a way to vectorize this function, although I expect it can be done.
In case your question is what I mean with vectorization:
a=1:10;
for n=1:9
if mod(a(n),3)==0
a(n)=a(n+1);
end
end
%vectorized:
b=1:10;
L1=mod(b,3)==0;
L2=[false L1(1:(end-1))];
b(L1)=b(L2);
thanks a lot for all this help

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