# how to sum a vector without sum func

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yuval ohayon on 27 Jul 2017
Commented: Jan de Jong on 31 Jul 2017
given this elements:19^3 −17^3 +15^3 −13^3 +11^3 −9^3 +7^3 −5^3 +3^3 −1^3 notice the sign changing 9 times with 10 element again without sum function\ anyone idea?
James Tursa on 27 Jul 2017
Edited: James Tursa on 27 Jul 2017
Maybe use plus and minus functions? What have you done so far?

Star Strider on 28 Jul 2017
The elements are cubed, so the signs are conserved.
This works:
v = [19^3 -17^3 +15^3 -13^3 +11^3 -9^3 +7^3 -5^3 +3^3 -1^3];
sum_v = v*ones(numel(v),1)
Check = sum(v) % Check
sum_v =
3970
Check =
3970
yuval ohayon on 28 Jul 2017
star its look like the right answer, the function ones(10,1} is a column vector?
Star Strider on 28 Jul 2017
Yes.
The ‘ones(length(v),1)’ call forms a (10 x 1) column vector.

Jan on 28 Jul 2017
v = 19^3 - 17^3 + 15^3 - 13^3 + 11^3 - 9^3 + 7^3 - 5^3 + 3^3 - 1^3;

Jan de Jong on 31 Jul 2017
Edited: Walter Roberson on 31 Jul 2017
Or a little more general:
val = [19:-2:1]'; sig = -cos(pi*[1:10]);
s = sig*val.^3;
yuval ohayon on 31 Jul 2017
Im sorry im not aware to -cospi×[1:10] Explain me please
Jan de Jong on 31 Jul 2017
It will give an alternating sequence to account for the sign change in the sum.

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