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Newsgroups: comp.soft-sys.matlab
Subject: Re: How can I determine a vector if I knew the angle between two
Date: Thu, 1 Dec 2011 04:10:09 +0000 (UTC)
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"Roger Stafford" wrote in message <jb6thh\$pu3\$1@newscl01ah.mathworks.com>...
>   There will be two solutions, v1 and v2:
>
>   a = atan2(u(2),u(1)); % Angle w.r. x-axis
>   v1 = [cos(a+theta),sin(a+theta)];  % Rotate plus theta
>   v2 = [cos(a-theta),sin(a-theta)];  % Rotate minus theta
>
> Both v1 and v2 will be unit vectors.
>
> Roger Stafford
- - - - - - - - -
The computation may be a little faster if you do it this way:

c = cos(theta); s = sin(theta); n = norm(u);
v1 = [u(1)*c-u(2)*s,u(2)*c+u(1)*s]/n;
v2 = [u(1)*c+u(2)*s,u(2)*c-u(1)*s]/n;

Roger Stafford
```