I'm hoping someone on here recognises this and has an answer, because I'm having serious memory issues.
About a year ago, I came across the following way of representing tensors of rank $n$ in matrix form, in a way similar to block matrices. Maybe this is just an alternative to block matrices actually.
Consider a simple $2 \times 2$ matrix definition:
I can represent a $2 \times 2 \times 2$ rank-3 tensor as a cuboid, but this is rather hard to show in a paper or proof, so a convenient notation exists that "splits up" the layers of the cuboid into $2 \times 2$ matrices, which can be flattened out and shown contiguously as follows:
Ditto a $2 \times 2 \times 2 \times 2$ rank-4 tensor can be represented as follows:
For both of these equalities, the notation on the left of the $=$ sign is the standard way of writing block matrices. However the explicit partition on the right is what I'm after: is there a particular name for this notation? Is it actually used somewhere to represent cuboids and other higher rank tensors or did I imagine it?
Thanks in advance if anyone has any info!