Please help me with evaluating double sums

2020 12 2
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Image Analyst
Image Analyst 2020-12-2

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You can do it with for loops, or with the meshgrid and sum functions:
x = 11 : 14
y = 2 : 5
% For loop way:
theSum = 0;
for i = 1 : 4
for j = 1 : 4
theSum = theSum + (x(i)^2 - 3 * y(j)^2 + x(i) * y(j)^3);
end
end
theSum
% Vectorized way using meshgrid:
[X, Y] = meshgrid(x, y);
theSum2 = sum(X(:) .^ 2 - 3 * Y(:) .^2 + X(:) .* Y(:) .^ 3)

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Dominic Marquez
Dominic Marquez 2020-12-2
Thanks, it turns out that my confusion comes from doing rectangular rule with a low number of subintervals. Since my number was so far off the actual one, I thought I was doing it wrong. Turns out I spent those hours frustrating over nothing.

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