Summation in a for loop without cumulitive
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I have a very simple question.
I want to summate the variable A for a certain interval + and - B.
for i=(b+1):length((a)-b)
C(i) = sum(a(i-b):(i+b));
end
This loop works, however the output that I get is a cumulative sum of all the previous. So I get an exponential increase. However I would like to just have the sum over the interval -b:b for all values of i. So no cummulation.
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Iain
am 26 Feb. 2014
C(i) = sum( a([i-b]:[i+b]) )
That puts into C(i), the sum of the (i-b)th index of a, to the (i+b)th index of a.
What you had, put into C(i), the sum of the (i-b)th index of a to (i+b)
2 Kommentare
Iain
am 26 Feb. 2014
If i+b is bigger than the length of a, you'll get that error.
length((a)-b) should be (length(a)-b)
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Jos (10584)
am 26 Feb. 2014
Another solution:
% hide the for-loop
% A is the array, B is a scalar
A = randperm(10)
B = 2
C1 = arrayfun(@(x) sum(A(x-B:x+B)), B+1:numel(A)-B)
% and yet another solution
cumA = cumsum(A)
C2 = cumA(2*B+1:end) - [0 cumA(1:end-2*B)]
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