Ah yes, I was thinking of ITK, my mistake. I don't follow what you are saying about using the *Arrays in the pipeline? Could there not be subclasses that function much as vtkMatrix4x4 does but just for vtkMatrixNxN type situations? And the main point is still that vtkMath functions should accept "reasonable" style matrices like this insetad of **array style data.

Yes, vtkDenseArray can be used as a matrix (or tensor) but my point is that none of the matrix functions currently use it. And it doesn't provide GetColumn/GetRow type functions. Everything that vtkMatrix4x4 has could be extended to more general size matrix/tensors. Could we just write wrappers for VNL classes (vnl_matrix, vnl_vector, etc)? Or even just use VNL directly since it is already packaged with VTK? What is the advantage to reimplementing everything from VNL in VTK?

This is critical to allow developers without core write access to get their contributions into a usable state for other users.

The library that needs to be linked to to use a class is also an important part of the documentation that is missing.

Is there a way in UserVoice to make a "sub vote"? I am thinking of a list of classes that people can vote for to indicate which ones need the most improvement.

Great! I think this is absolutely the most important thing for promoting usage of VTK. I think EVERY function needs to contain:
1) What does the function do? This is currently usually stated, but the statements are usually quite brief and could use some expanding.
2) What does EVERY variable in its argument list represent/mean? Which ones are inputs? Which ones are outputs? This is the most important thing for new users.