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how to sum a vector without sum func

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yuval ohayon
yuval ohayon 2017-7-27
评论： Jan de Jong 2017-7-31
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?
  1 个评论
James Tursa
James Tursa 2017-7-27
编辑：James Tursa 2017-7-27
Maybe use plus and minus functions? What have you done so far?

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采纳的回答

Star Strider
Star Strider 2017-7-28
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
  2 个评论
yuval ohayon
yuval ohayon 2017-7-28
star its look like the right answer, the function ones(10,1} is a column vector?
Star Strider
Star Strider 2017-7-28
Yes.
The ‘ones(length(v),1)’ call forms a (10 x 1) column vector.

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更多回答（2 个）

Jan
Jan 2017-7-28
What about:
v = 19^3 - 17^3 + 15^3 - 13^3 + 11^3 - 9^3 + 7^3 - 5^3 + 3^3 - 1^3;
Jan de Jong
Jan de Jong 2017-7-31
编辑：Walter Roberson 2017-7-31
Or a little more general:
val = [19:-2:1]'; sig = -cos(pi*[1:10]);
s = sig*val.^3;
  2 个评论
yuval ohayon
yuval ohayon 2017-7-31
Im sorry im not aware to -cospi×[1:10] Explain me please
Jan de Jong
Jan de Jong 2017-7-31
It will give an alternating sequence to account for the sign change in the sum.

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