Algorithm 4.

Implementation of Projection Operator Π_𝒩(Z)

1:	for all i, j, k do
2:	X ← Z(i, j, k)
3:	(λ, V ) ← Eig(XTX) ▷ compute eigenvalues and eigenvectors [13]
4:	$\mathrm{\sum }\leftarrow \text{diag}(\sqrt{\lambda })$
5:	if Tr (Σ) > 1 then
6:	Σp ← min(1, Σ) ▷ element-wise minimum
7:	X ← XV Σ+ΣpV T
8:	end if
9:	Z(i, j, k) ← X
10:	end for