Affine transforms - matrix algebra

Martin Desruisseaux martin.desruisseaux at
Thu Jul 12 05:20:35 PDT 2012

Le 12/07/12 14:08, Kirill Prazdnikov a écrit :
> Transformation matrix consist of four vectors. In case of affine, it 
> is coordinates of local orts + translation.
> Accessing this vectors is the most get/set use-case.
> I can not imagine where accessing individual matrix values could be 
> used (useful) at all.
> Does anybody uses it ?

Well, then intend is to access the vectors by looping over (row,column) 
indices. In the current API, we can only access individual matrix values 
through named properties. This means that we can not use loops neither 
parametrized methods. For example in order to compute the magnitude of a 
vector (my previous email about "square root of the sum of ..." was a 
complicated way to said exactly that), we have to:

  * explicitly sum every terms as in sqrt(mxx*mxx + mxy*mxy + mxz*mxz);
  * duplicate the above code for every rows.

While I admit that a loop doesn't save much in this example, some other 
use case are a bit more complicated. And the problem of duplicated code 
for every vector (row) remain. If a 'get(row, column)' method is 
provided, then a user can compute a vector magnitude in a single method 
where the vector number (row index) is given as a method argument.


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