Add cross product operator

[mfzmullen]

Takes in two operators of size A0 x ... x An x 3 (or 2) and size B0 x ... x Bn x (3 or 2) with matching batch sizes and computes the cross product. If both input operators have size = 2 on the last dimension, the size of the output's last dimension is still 3. This is contrary to the NumPy implementation which drops the rank of the output by 1 if both inputs are in-plane vectors. Doing so in MatX does not seem straightforward since Rank is a static method and we may not know the sizes of A and B (e.g. 2 or 3 on the last dimension) at the time the rank is determined, but those sizes affect the rank of cross if we followed NumPy's approach. The alternative would be to have the output size equal 1 on the last dimension for two size=2 inputs and only contain the z-component of the cross product, since the other two components of cross are 0.

[cliffburdick]

Looks great! Thanks for doing this

[cliffburdick]

/build

[cliffburdick]

Hi @mfzmullen, I apologize I didn't see this earlier, but the documentation needs to be updated:

/home/jenkins/workspace/unit-tests/include/matx/operators/cross.h:188: error: argument 'OpA' of command @param is not found in the argument list of matx::cross(const OpA &A, const OpB &B) (warning treated as error, aborting now)