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CIS750 – Seminar in Advanced Topics in Computer Science Advanced topics in databases – ... - page 22 / 30

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VQ Design – The Generalized Lloyd Algorithm (GLA)

It produces a locally optimal codebook from a training sequence, T. It starts with an initial codebook and iteratively improves it.

                                         Lloyd Iteration

Given a codebook Cm={yi} generate an improved codebook Cm+1 as follows:

Partition T into cells Rj using the Nearest Neighbor Condition:

                     Ri={x : d(x,yi) d(x,yi);   ji}

Using the Centroid Condition compute the centroids of the cells just found to obtain the new codebook, Cm+1={cent(Ri)}

Compute the average distortion for Cm+1 , Dm+1. If the fractional drop (Dm- Dm+1) / Dm is below a certain threshold stop, else continue with mm+1

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