Compute double sum or double integral throug sum

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.

[Adam]

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]

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

Answer 1

[Honglei Chen]

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

[F.O]

Could you explain more why we should use transpose here and what this the sum here works?

[Guillaume]

See Add row and column vector

Answer 2

[Roger Stafford]

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