I just had my last Linear Algebra class, and I didn't get a chance to ask the one question that has been bugging me ever since we started in earnest with matrices. Why aren't there cube matrices? I mean, mathematical entities where numbers are 'laid out' in 3d not in 2d (not quite mathematically rigorous, but you get the idea). Obviously one could do this with successive matrices, but I wonder if more is to be gained by studying this object as a whole. Is this a thing? Is there an obvious reason I'm missing as to why there is nothing to gain by doing this?