how to sum a vector without sum func

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]

Maybe use plus and minus functions? What have you done so far?

Answer 1

[Star Strider]

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]

star its look like the right answer, the function ones(10,1} is a column vector?

[Star Strider]

Yes.

The ‘ones(length(v),1)’ call forms a (10 x 1) column vector.

Answer 2

[Jan]

What about:

v = 19^3 - 17^3 + 15^3 - 13^3 + 11^3 - 9^3 + 7^3 - 5^3 + 3^3 - 1^3;

Answer 3

[Jan de Jong]

Or a little more general:

val = [19:-2:1]'; sig = -cos(pi*[1:10]);
s = sig*val.^3;

[yuval ohayon]

Im sorry im not aware to -cospi×[1:10] Explain me please

[Jan de Jong]

It will give an alternating sequence to account for the sign change in the sum.