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TESI DOCTORAL - La Salle

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3.2. Random hierarchical consensus architectures<br />

SERT RHCA (sec.)<br />

PERT RHCA (sec.)<br />

10 2<br />

10 1<br />

10 0<br />

10 1<br />

10 0<br />

10 −1<br />

s : number of stages<br />

10 7 6 5 4 4 3 3 2 2 1<br />

2 3 4 5 6 10 11 32 33 798 1596<br />

b : mini−ensemble size<br />

(a) Serial estimated running time<br />

s : number of stages<br />

10 7 6 5 4 4 3 3 2 2 1<br />

2 3 4 5 6 10 11 32 33 798 1596<br />

b : mini−ensemble size<br />

(c) Parallel estimated running time<br />

CSPA<br />

EAC<br />

HGPA<br />

MCLA<br />

ALSAD<br />

KMSAD<br />

SLSAD<br />

CSPA<br />

EAC<br />

HGPA<br />

MCLA<br />

ALSAD<br />

KMSAD<br />

SLSAD<br />

SRT RHCA (sec.)<br />

PRT RHCA (sec.)<br />

10 2<br />

10 1<br />

10 0<br />

10 1<br />

10 0<br />

10 −1<br />

s : number of stages<br />

10 7 6 5 4 4 3 3 2 2 1<br />

2 3 4 5 6 10 11 32 33 798 1596<br />

b : mini−ensemble size<br />

(b) Serial real running time<br />

s : number of stages<br />

10 7 6 5 4 4 3 3 2 2 1<br />

2 3 4 5 6 10 11 32 33 798 1596<br />

b : mini−ensemble size<br />

(d) Parallel real running time<br />

CSPA<br />

EAC<br />

HGPA<br />

MCLA<br />

ALSAD<br />

KMSAD<br />

SLSAD<br />

CSPA<br />

EAC<br />

HGPA<br />

MCLA<br />

ALSAD<br />

KMSAD<br />

SLSAD<br />

Figure 3.7: Estimated and real running times of the serial RHCA on the Zoo data collection<br />

in the diversity scenario corresponding to a cluster ensemble of size l = 1596.<br />

Conclusions regarding the computationally efficiency of RHCA<br />

The observation of the results obtained across the four diversity scenarios allow drawing<br />

several conclusions (together with the experiments presented in appendix C.2) as regards<br />

the computational efficiency of hierarchical and flat consensus architectures:<br />

– hierarchical consensus architectures can constitute a feasible way to obtain a consensus<br />

clustering solution in cases where one-step consensus is not affordable, which<br />

ultimately depends on the size of the cluster ensemble, the characteristics of the consensus<br />

function and the computational resources at hand.<br />

– as expected, parallel RHCA are highly efficient, being faster than flat consensus even<br />

in low diversity scenarios.<br />

– serial RHCA implementations become computationally competitive in medium to high<br />

diversity scenarios.<br />

– depending on the characteristics of the consensus function(s) employed for conducting<br />

clustering combination, large variations of the overall execution time of consensus<br />

architectures are observed.<br />

62

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