# Double sum with upper limits

4 vues (au cours des 30 derniers jours)
H Lange le 2 Mar 2020
Commenté : Luna le 3 Mar 2020
Hi
I am trying to do the following calululation in matlab:
But I do not how how to do the two sums in the front. Our data (d) is a 67x120 array.
Any suggestions would be appreciated :)
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darova le 2 Mar 2020
Luna le 2 Mar 2020
Modifié(e) : Luna le 2 Mar 2020
What have you done so far as coding? And what is d?

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### Réponse acceptée

Guillaume le 2 Mar 2020
Modifié(e) : Guillaume le 2 Mar 2020
s = (1:size(d, 1)).';
result = sum(sum(d .* cos(s))) / sum(cos(s));
Loops not needed, they're just a waste of time.
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Guillaume le 2 Mar 2020
Yes, I made a mistake, there was a sum missing in the denominator. I assumed that the could be taken out of the double sum, i.e. it's over the whole range. It's not clear and we didn't get an answer to Darova's question. So, my code implement:
If it's a partial sum as you think, then:
s = (1:size(d, 1)).';
result = sum(sum(d .* cos(s) ./ cumsum(cos(s))));
which implements
Luna le 3 Mar 2020
You are right.

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### Plus de réponses (1)

Luna le 2 Mar 2020
Maybe something like that would help:
d = rand(67,120);
sum_of_cos_s = 0;
result = 0;
for s = 1:67
for j = 1:120
sum_of_cos_s = sum_of_cos_s+cos(s);
result = result + (d(s,j)*cos(s))/sum_of_cos_s;
end
end
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