How to sum over each n-th element in an array ?

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Agnivo Gosai
Agnivo Gosai 2019-9-30
编辑： Stephen23 2019-9-30
I have a 1 x 108108 array (named output) and I am trying to calculate the sum of elements in this fashion : a1 = sum (1st element + 1002th element + 2003th element +....+ (108108-1001)th element), for each 1008th element after the beginning one. The next sum would be a2 = sum (2nd element + 1003th element + 2004th element....+(108108-1001)th element) and so on till, a1001 = sum (1001th element + 2002th element + 3003th element +....108108th element). Afterwards, I want to collect a1,a2,a3...,a1001 into an array.
Could somebody point me to some documentation that will help me to do this ?
Thanks

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Stephen23
Stephen23 2019-9-30
编辑：Stephen23 2019-9-30
Just use reshape:
>> b = sum(reshape(a,1001,[]),2);
and checking the output:
>> b(1)
ans = -6343.8
>> sum(a(1:1001:end))
ans = -6343.8
>> b(2)
ans = -6345.5
>> sum(a(2:1001:end))
ans = -6345.5

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