Algorithm 3.

Noiseless algorithm

Require: X ∈ Rn×p
1:	Set Imax = Imin = ∅.
2:	repeat
3:	Generate a p × m random matrix G with independent 𝒩(0, 1) entries.
4:	Form the product XG.
5:	Find the indices of the max $I_{\text{max}}^{\prime }$ and min $I_{\text{min}}^{\prime }$ in each column of XG.
6:	Set $I_{\text{max}}\leftarrow I_{\text{max}}\cup I_{\text{max}}^{\prime },I_{\text{min}}\leftarrow I_{\text{min}}\cup I_{\text{min}}^{\prime }$.
7:	until $I_{\text{max}}^{\prime },I_{\text{min}}^{\prime }$ adds nothing to $I_{\text{max}}^{\prime },I_{\text{min}}^{\prime }$.
8:	Return H = XImax∪Imin.