What's the meaning of "reuse space"?

Question

I'm reading this.

$\quad \;\;$

What's the meaning of reuse space in here?

Answer 1

That you don't create new matrices $D^{(n)}$ but just modify the values in the one matrix. Well, not in one matrix but you have two where one is the previous one ($D^{(n - 1)}$) and the second is the one you compute. When a new $D^{(n)}$ is computed, it becomes $D^{(n - 1)}$ in the next iteration and the previous $D^{(n - 1)}$ (now $D^{(n - 2)}$) becomes a space for the new $D^{(n)}$.