# More Efficient ismember Calculation

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Ayden Clay on 16 Apr 2020
Commented: Ayden Clay on 20 Apr 2020
Hello, I'm working on an interpolation for a specific project that I'm working on and have managed to produce a very fast interpolation function for N-D array for042. There is one final bottleneck that is taking up 84% of the total run-time of the program. Inserted are the profiler and exemplar code, any and all optimizations are greatly appreciated, but the particular line is obvious from the profiler.
alpha = -5:5:30;
mach = 1:6:25;
beta = -5:2.5:5;
num = zeros(length(alpha),length(mach),length(beta));
for cnt = 1:numel(alpha)
for cnt1 = 1:numel(mach)
for cnt2 = 1:length(beta)
num(cnt,cnt1,cnt2) = 3*alpha(cnt)+mach(cnt1)/2+beta(cnt2);
end
end
end
for cnt2 = 1:length(beta)
data.for006{cnt2}.cd = num(:,:,cnt2);
end
Is an example of the data set that we're working with.
And the line in question from the profiler is part of this block:
a = zeros(1,2^size(CURRENT,1)-1);
curridx = zeros(1,size(CURRENT,1));
for cnt = 1:(2^size(CURRENT,1))
change = find((rem(cnt-1,2.^(0:size(CURRENT,1)-1))==0)==1);
curridx(change) = 1*curridx(change)==0;
idx = lidx.*(curridx==0) + uidx.*(curridx==1);
chkvals = zeros(1,length(idx));
for cnt1 = 1:length(idx)
B = RANGES{cnt1};
chkvals(cnt1) = B(idx(cnt1));
end
chkvals = [chkvals(2),chkvals(4:end)];
% INEFFICIENT LINE %
a(cnt) = DATA.for042{find(ismember(DATA.permutation,chkvals,'rows'))}.cn(sub2ind_a(siz,idx));
end
##### 11 CommentsShowHide 10 older comments
Ayden Clay on 20 Apr 2020
ahh, I understand! I've now, I believe, moved as much as I can outside of loops.

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### Accepted Answer

Steven Lord on 16 Apr 2020
What's the most time consuming part of that line that you've identified as the bottleneck? Is it the ismember call, the indexing into DATA.for042, the indexing into the result of that indexing to retrieve part of the cn field, or the assignment into a section of a? To tell, break that into four parts (for performance profiling purposes.)
ind = ismember(DATA.permutation,chkvals,'rows');
data1 = DATA.for042{ind};
data2 = data1.cn(sub2ind_a(siz,idx));
a(cnt) = data2;
My guess is that the ismember call still might be the most time consuming part of that process, but it's not going to be all 83.4% of the total runtime of your code.
##### 6 CommentsShowHide 5 older comments
Ayden Clay on 20 Apr 2020
I completely agree, I've implemented a large number of those changes too (there may be more), I've tried to remove some of the for loops in favour of vector operations. There is still some work to be done, but this is much closer to what I needed. Thank you.

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