Re: Atan2 and angle between vectors

[Dirk Laurie <dirk.laurie@...>]

>>> To calculate the angle beteween the two vectors, you sould do:
>>>
>>> math.atan2(b[2],b[1]) - math.atan2(a[2],a[1])
>>>
>>>
>>
>> Not that simple.  That could give anything between ± 2 pi, whereas angle should
>> be between ± pi.
>
> By adding/subtracting 2pi accordingly one can make result to be in (-pi,+pi].
>

The formula

     math.atan2 (a[1]*b[2]-a[2]*b[1],a[1]*b[1]+a[2]*b[2])

makes only one call to math.atan2, requires no post-processing, and has slightly
better roundoff properties.