Questions about Eq.8

[OnlyForWW]

I would like to ask how n^2 in Eq.8 was obtained, or could you please explain in detail the calculation process of Eq.8. Thank you very much

[HantingChen]

Sorry for the mistake, the n^2 should be (2n+1)^2. The Eq.6 is summed accross two dimesnion i and j, and each dimension has 2n+1 values. Therefore, the computation complexity is (2n+1)^2.