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Invisible <voi### [at] dev null> wrote:
> >> ...except that then I'd have to somehow remember the correct way to do
> >> matrix multiplication. (Something which I never get right with more than
> >> 50% probability...)
> >
> > Then you just end up using left-handed coordinates for your cross product
> > rather than right-handed. In other words, it only affects the sign of the
> > result.
> Oh, does it?
> With general matrix multiplication, getting it wrong tends to really
> mess things up. But in the specific case of a cross product, maybe it
> doesn't...
If you try to calculate A*B of two square matrices in the wrong order
(ie. A columns times B rows instead of the other way around), what you end
up doing is calculating B*A. With a cross-product it means that you are
using the opposite winding, thus reversing the resulting vector. The end
result is still correct, just pointing to the opposite direction of what
you wanted.
--
- Warp
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>> With general matrix multiplication, getting it wrong tends to really
>> mess things up. But in the specific case of a cross product, maybe it
>> doesn't...
>
> If you try to calculate A*B of two square matrices in the wrong order
> (ie. A columns times B rows instead of the other way around), what you end
> up doing is calculating B*A. With a cross-product it means that you are
> using the opposite winding, thus reversing the resulting vector. The end
> result is still correct, just pointing to the opposite direction of what
> you wanted.
Well, in my case I'm merely trying to construct a system of
perpendicular vectors, so I'm not really bothered *what* they are, so
long as they're actually perpendicular. Getting the cross product
epically wrong like I did prevents this from happening...
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On 01/22/10 01:33, Invisible wrote:
> Neeum Zawan wrote:
>
>> Oh dear. Use the determinant form - easiest to remember:
>>
>> http://en.wikipedia.org/wiki/Cross_product#Matrix_notation
>
> ...except that then I'd have to somehow remember the correct way to do
> matrix multiplication. (Something which I never get right with more than
> 50% probability...)
I fail to see why you'd need to know how to do matrix multiplication.
Calculating determinants is a different procedure.
--
If you think nobody cares, try missing a couple of payments.
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