# Easy for loop question

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Ron on 18 Aug 2014
Commented: Ron on 18 Aug 2014
I'm trying to make a simple For Loop:
for i=1:603
if A(i,2)>((A(i-1,2)+A(i+1,2))/2)*10
A(i,:)=[];
and i'm getting the error:
"Subscript indices must either be real positive integers or logicals."
I don't understand why, since i is an integer.
Thanks

Edited: Adam on 18 Aug 2014
i - 1
will be 0 in the first pass through the loop. Indices must be positive integers, i.e. 1 or greater. Matlab indexes arrays from 1, not from 0 as e.g. C++ does.
Ron on 18 Aug 2014
Thank you !

Evan on 18 Aug 2014
Edited: Evan on 18 Aug 2014
i must be a real, positive integer. Because i starts at 1, and you reference A(i-1,2), your first iteration will try to access A(0,2), and 0 is not a proper matrix index under MATLAB's conventions.
To solve this, either adjust your indexing so that you access A(i+1,:) or change your range to i = 2:603+1
Ron on 18 Aug 2014
Thank you !!

Guillaume on 18 Aug 2014
As others have said, the issue is from A(i-1,2) that is not valid for i = 1.
There's a second issue that you are deleting rows as you are iterating over them so in all likelyhood, you'll hit an 'index exceeds matrix dimensions' before the end of the loop because you no longer have 603 rows.
Ron on 18 Aug 2014
You are right !!! thanks a-lot !!!

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