Compute double sum or double integral throug sum

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F.O
F.O 2017-10-30
回答： Roger Stafford 2017-10-30
x=[-20:0.2:10];
y=[-10:0.2:5];
u2=-3*exp(-sqrt(x.^2+y.^2)/2)
I want to sum this function from y=1 to the number of elements of y vector then the sum of this result from x=1 to the number of elements in x. IT is actually a double integral in form of sum.
  2 个评论
Adam
Adam 2017-10-30
You want to sum from y = 1 up to the number of elements in y even though y begins at -10 and runs to 5? How is that expected to work exactly?
F.O
F.O 2017-10-30
编辑：F.O 2017-10-30
Here we are dealing with the position of the elements not the elements themseves. Maybe to use for loop command here. IT is actually a double integral which I should integrate with respect to from y= -10to y=5in the first step then with respect to x from x=-20 to x=10 I have dx=0.2 dy=0.2

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采纳的回答

Honglei Chen
Honglei Chen 2017-10-30
If the ultimate goal is to compute the integral, you can consider using integral2
https://www.mathworks.com/help/matlab/ref/integral2.html
If you have to do it with sum, then since you already computed u2 for all values, it is just
x=[-20:0.2:10]; y=[-10:0.2:5]'; u2=-3*exp(-sqrt(x.^2+y.^2)/2);
sum(u2(:))*0.2*0.2
Note that you have to transpose x or y so it forms a grid
HTH

更多回答（1 个）

Roger Stafford
Roger Stafford 2017-10-30
[X,Y] = meshgrid(x,y);
M = -3*exp(-sqrt(X.^2+Y.^2)/2);
S = sum(M(:))*.2*.2; % The desired sum

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