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TESI DOCTORAL - La Salle

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4.2. Flat vs. hierarchical self-refining<br />

1. Given a cluster ensemble E containing l<br />

⎛<br />

components:<br />

⎞<br />

λ1<br />

⎜<br />

⎜λ2<br />

⎟<br />

E = ⎜ ⎟<br />

⎝ . ⎠<br />

and a pre-computed consensus clustering solution λc, compute the φ (NMI) between<br />

λc and each of the components of the cluster ensemble, that is:<br />

λl<br />

φ (NMI) (λc, λk) , ∀k =1,...,l<br />

2. Generate an ordered list Oφ (NMI) = {λ<br />

φ (NMI) 1, λ φ (NMI)2,...λφ (NMI)l} of cluster ensemble<br />

components ranked in decreasing order according to their φ (NMI) with respect<br />

λc.<br />

3. Create a set of P select cluster ensembles Epi<br />

nents of Oφ (NMI):<br />

Epi =<br />

⎛<br />

λ<br />

φ (NMI)<br />

⎜<br />

⎝<br />

1<br />

λ<br />

φ (NMI) 2<br />

⎞<br />

⎟<br />

.<br />

⎟<br />

⎠<br />

where pi ∈ (0, 100) , ∀i =1,...,P.<br />

λ φ (NMI) ⌊ p i<br />

100 l⌉<br />

pi<br />

by compiling the first ⌊ 100l⌉ compo-<br />

4. Run a (flat or hierarchical) consensus architecture based on a consensus function F<br />

on Epi , obtaining a self-refined consensus clustering solution λc p i .<br />

5. Apply the supraconsensus function on the non-refined consensus clustering solution<br />

λc and the set of self-refined consensus clustering solutions λc p i , i.e. select as the<br />

final consensus solution the one maximizing its φ (ANMI) with respect to the cluster<br />

ensemble E.<br />

Table 4.1: Methodology of the consensus self-refining procedure.<br />

4.2 Flat vs. hierarchical self-refining<br />

In this section, we present several experiments regarding the application of the consensus<br />

self-refining procedure described in section 4.1 on the consensus clustering solutions output<br />

by the three consensus architectures described in chapter 3. In all cases, our main interest<br />

is focused on analyzing the qualities of the clusterings obtained by the proposed self-refining<br />

procedure, not on evaluating the computational aspects of the self-refining process, as the<br />

decision regarding whether it is implemented according to a hierarchical or a flat consensus<br />

architecture can be efficiently made using the running time estimation methodologies<br />

proposed in chapter 3.<br />

The experiments conducted follow the design described next.<br />

112

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