[Gridflow-dev] geometry, cross products, matrix inversions...

[mescalinum at gmail.com]

Il 24/11/2011 23:10, mescalinum at gmail.com ha scritto:
> Il 21/11/2011 09:07, Mathieu Bouchard ha scritto:
>> Le 2011-11-19 à 22:32:00, mescalinum at gmail.com a écrit :
>>
>>> it involves a 3x3 times 3x1 inner product, but requires some 
>>> #pack/#unpack trickery. would you do it in some alternative way?
>>
>> use [# cross], added 2 minutes ago. Should be much faster than any of 
>> my 3 first solutions.
>>
>>> also, what about computing the adjoint[1] of a matrix?
>>> [1] http://en.wikipedia.org/wiki/Adjugate_matrix
>>
>> a fast way would use [# cross] preceded by some amount of preparation.
>> Using two 3x3 matrices, [# cross] will do 3 cross products.
>>
>> [#store] allows to easily select rows from a matrix (but not 
>> columns). You just give it a column-matrix of indices (3 1 # ...).
>>
>> Post your patch when you're done. :)
>
> could be an example of using [# cross] (other than [# cross] used for 
> doing cross products!)

actually there was an error in the patch.
I corrected it; I also added a little proof, that is: A*adj(A) is always 
equal to det(A)*I for every A
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