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From: NIcholas on 7 Jun 2010 11:59
I have a vector A and I want to search A for the first value larger than some constant c, starting at index i.

Is there a quicker way than the following command?
find(A(i:end)>c,1,'first')

I assume that it is copying the array A(i:end) and then doing the computation, which will be slow if the first element is very close to the front.

Thanks,
Nick
From: Bruno Luong on 7 Jun 2010 12:26
"NIcholas " <dsfadfa(a)aol.com> wrote in message <huj50b$pq5$1(a)fred.mathworks.com>...
> I have a vector A and I want to search A for the first value larger than some constant c, starting at index i.
>
> Is there a quicker way than the following command?
> find(A(i:end)>c,1,'first')
>
> I assume that it is copying the array A(i:end) and then doing the computation, which will be slow if the first element is very close to the front.

I can only think of mexing.

More generally, you could use the solution proposes here

http://www.mathworks.com/matlabcentral/fileexchange/24576-inplacearray-a-semi-pointer-package-for-matlab

function testfind(i)

A=rand(1,1e7);

tic;
find(A>0.5,1,'first');
toc % Elapsed time is 0.055850 seconds.

tic;
find(A(i:end)>0.5,1,'first');
toc % Elapsed time is 0.151338 seconds.

tic;
ai=inplacearray(A,i);
find(ai>0.5,1,'first');
releaseinplace(ai);
toc %Elapsed time is 0.063139 seconds.

end
% Bruno
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