How can I calculate a double sum?

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"

[Solarmew]

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]

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?