How can I calculate a double sum?

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Solarmew 2015-5-24

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https://ww2.mathworks.cn/matlabcentral/answers/218323-how-can-i-calculate-a-double-sum

评论： Walter Roberson 2015-5-24

something like this

function test
syms u(x,t,r)
u(x,t,r) = x + t + r ;
tl = 0:2:4;
rl = 1:2:5;
ur = sum(u(x,tl,rl))
end

it works if i put in "r" instead of "rl" in the sum, but I want to sum over both "t" and "r"

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Solarmew 2015-5-24

编辑：Solarmew 2015-5-24

在 MATLAB Online 中打开

got something, but is there a more elegant way then this?

function test2
syms u(x,t,r) u(x,r)
u(x,t,r) = x + t + r ;
tl = 0:1;
rl = 1:2;
ur(x,r) = sum(u(x,tl,r));
sum(ur(x,rl))
end

Walter Roberson 2015-5-24

Are you wanting each t with the r corresponding in the same position, or are you wanting the combinations, first t combined in turn with each of the elements of r, second t combined with each element of r, and so on? Should the number of summations be according to length of t which would have to be the same as length of r, or should the number be length of t multiplied by length of r?

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