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From: Dmitriy on 2 Feb 2010 12:57
Have two sorted arrays DTime (size N~6000) and T (~ size 20*N)

For each element i in DTime want to find the last element j in T s.t. DTime(i) >T(j)

I can solve this task with
for i=1:length(DTime)
res(i)=find(DTime(i)>T,1)-1;
end

However, it is inefficient, as on each iteration a large matrix T is passed to find().

This problem is pretty standard. I wonder if there is a better solution?

PS: I ran an experiment. Seems that size of T is the main slowing factor for find()

A=zeros(1,10000000);A(1,5)=1;
tic
for i=1:100; find(A==1,1);end
toc
tic
for i=1:100; find(A==1);end
toc
%%
A(1,5)=0;A(1,5000000)=1;
tic
for i=1:100; find(A==1,1);end
toc
%%
A=zeros(1,5000000);A(1,5000000)=1;
tic
for i=1:100; find(A==1,1);end
toc

Elapsed time is 2.144091 seconds.
Elapsed time is 2.770985 seconds.
Elapsed time is 2.502952 seconds.
Elapsed time is 1.894031 seconds.
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