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Why doesn't atan2 (u,v) give me the right angle of two simple vectors?

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farzad
farzad on 4 Jun 2019
Edited: Jan on 28 Jun 2019
Hi All
I was using the atan2(u,v) to calculate the angles between vectors, untill I checked it for
u=[0,0,0]
v= [1,1,1]
doing :
teta=atan2(norm(cross(u,v)),dot(u,v));
I get teta = 0
I am expecting teta = 54 °
where am I going wrong ?

  1 Comment

KSSV
KSSV on 4 Jun 2019
Why do you expect it to be 54? IT is showing correct.
teta=atan2d(norm(cross(u,v)),dot(u,v));

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Accepted Answer

Jan
Jan on 4 Jun 2019
Edited: Jan on 4 Jun 2019
Of course this code replies 0. If one of the vectors is the Null vector, there cannot be an angle different from 0.
So the only problem is that you expect 54°. atan2 will not reply degrees at all, but radians.
u = [1, 0, 0]
v = [cos(0.123), -sin(0.123), 0]
atan2(norm(cross(u,v)),dot(u,v))
>> 0.1230 % As expected

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