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An assignment of vectorization

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Reuben Addison
Reuben Addison on 2 Feb 2019
Closed: John D'Errico on 14 Oct 2021
Say you have two column vectors vv and ww, each with 7 elements (i.e., they have dimensions 7x1). Consider the following code:
z = 0;
for i = 1:7
z = z + v(i) * w(i)
end
A) z = sum (v .* w);
B) z = w' * v;
C) z = v * w;
D) z = w * v;
According to the solutions, answers (A) AND (B) are the right answers, can someone please help me understand why?
  6 Comments
Sinehan S
Sinehan S on 29 Nov 2020
Edited: Sinehan S on 29 Nov 2020
In question they said that each column vector v and w as 7x1 dimension.
They gave v(i)*w(i). So, we cannot multiply 7*1 dimension and 7*1 dimension.
So, we should take transpose for anyone v(i) or w(i).
Then, only we get (1*7)(7*1) and (7*1)(1*7)dimension.
Finally, we get solution by multiply them.
Amr Soror
Amr Soror on 14 Oct 2021
for A) x .* y
Element-by-element multiplication. If both operands are matrices, the number of rows and columns must both agree, or they must be broadcastable to the same shape.

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