The reason for concatenation of the three adjacency matrices

[QEASONT]

Excuse me, could you please talk about the concatenation of the three adjacency matrices?

[XBR-1111]

I'm also curious about that.

[Muhongfan]

Same here!
Questions on:
1). how do you define the whole matrix with three sub-matrices and why do you design it like so, are there any references?
2). could you plz explain more on the A_{TC} as to why it is nonzero for the previous and next time steps are the same node, does it mean that the A_{TC} should be a diagonal matrix?