How to Vectorize this Code?

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Krishan Bansal
Krishan Bansal on 21 Sep 2022
Commented: Krishan Bansal on 21 Sep 2022
I have this 147000 x 3 array, where each index represents a 3D vector. I want to use the vector at each index to find the angle between it and a predefined vector "b0" [ 0 1 0], this results in a 147000 x 1 array where each index has a single angle. I have been able to do this by using a normal for loop, however I was wondering if there was a way to vectorize this so it will be faster. I have been trying, but it either says that it can't do the dot product because arrays are of incompatible size, or it will only calculate the angle of the first index, then copy that 147000 times into the Nx1 array.
Thanks for any help.
  4 Comments
Krishan Bansal
Krishan Bansal on 21 Sep 2022
@Matt J ok the code is just:
n3Array = squeeze(Orientation4D(:, 1, 1,1:3));
N = length(n3Array);
b0angles = zeros(N,1);
for i = 1:N
b0angles(i) = rad2deg(acos(dot(n3Array(i,:), b0)/(norm(n3Array(i,:)) * norm(b0))));
end

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Accepted Answer

Matt J
Matt J on 21 Sep 2022
Edited: Matt J on 21 Sep 2022
n3Array=normalize(n3Array,2,'n');
b0=b0/norm(b0);
b0angles=acosd(n3Array*b0);
  11 Comments
Krishan Bansal
Krishan Bansal on 21 Sep 2022
@James Tursa That worked perfectly, I forgot to use the normalized version of n3 I think. Thanks so much! This is super concise and efficient code.

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