# How to accumulate values into a variable using for loops?

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NH on 16 Apr 2013
Hello,
I have an array that contains 1597 values. Let's call that X. I want to create a second array, Y, that should act as the following:
Y(1) = (X(1) + X(2))/(constant)
Y(2) = (X(2) + X(3))/(constant) + Y(1)
Y(3) = (X(3) + X(4))/(constant) + Y(2)
Y(4) = (X(4) + X(5))/(constant) + Y(3)
..and so on, until the last one:
Y(1596) = (X(1596) + X(1597))/(const) + Y(1595)
My code, which does not return an error, but also does not produce the correct values for Y, is as follows:
Y = zeros(1,length(X)-1);
Y(1) = (X(1)+X(2))/(constant);
i = 1:length(X);
for c = 1:length(X)-2
Y(c+1) = (X(c+1)+X(c+2))/(constant) + Y(i(c));
end
As stated above, the results I'm getting are not accurate (I'm comparing with results obtained through Excel, which are definitely correct). If anyone can please tell me where I'm going wrong, I would greatly appreciate it. If this description isn't clear enough, please let me know and I will try to clarify. Any help is greatly appreciated.
Thanks.

Yao Li on 16 Apr 2013
Edited: Yao Li on 16 Apr 2013
Y(c+1) = (X(c+1)+X(c+2))/(constant) + Y(c);
Also, actually, you don't need the parameter i.
NH on 16 Apr 2013
Problem solved. Careless mistake: started reading original values at wrong point, causing a slight offset. Thanks for your help and patience.

Andrei Bobrov on 16 Apr 2013
Y = cumsum(conv(X,[1 1]/constant,'valid'));