[ODE] why is dMatrix3 4x3 instead of 3x3?

[Selcuk SENKUL]

hi,

I am very new to ode and I noticed something strange. The data structure
dMatrix3, explained as a 3x3 matrix, is actually a 4x3 matrix. An when you 
use this matrix to set the rotation of a geom, the top-left 3x3 matrix is filled
and the rest is zero. So until now, there should be no problem, but when you 
get the rotation of a geom, the result comes as a dReal* and there are actually
12 values instead of 9. So you have to jump the 4th and 8th numbers to get the 
correct 3x3 matrix. I read the documentation but was not able to find anything
about this. My guess is that the last colum is used in internal computations?
So can someone explain why things are this way. thanks.

Selcuk