CLSI - computes a rank-L approximation of the input matrix 
  using the Clustered Latent Semantic Indexing Method [1]
    [X, Y]=CLSI(A, CLUSTERS, L, FUNC, ALPHA_VAL, SVD_METHOD) 
    computes the rank-L approximation X*Y of the input matrix 
    A with the Clustered Latent Semantic Indexing Method [1], 
    using the cluster structure information from CLUSTERS.
    FUNC denotes the method used for the selection of the 
    number of factors from each cluster. Possible values for 
    FUNC:
        - 'f': Selection using a heuristic method from [1] 
          (see KS_SELECTION). 
        - 'f1': Same as 'f' but use at least one factor 
          from each cluster. 
        - 'equal': Use the same number of factors from 
          each cluster. 
    ALPHA_VAL is a value in [0, 1] used in the number of 
    factors selection heuristic [1]. Finally, SVD_METHOD 
    defines the method used for the computation of the SVD 
    (svds or propack).
 
    REFERENCES: 
    [1] D. Zeimpekis and E. Gallopoulos. CLSI: A Flexible 
    Approximation Scheme from Clustered Term-Document Matrices. 
    In Proc. 5th SIAM International Conference on Data Mining, 
    pages 631–635, Newport Beach, California, 2005.
 
  Copyright 2011 Dimitrios Zeimpekis, Eugenia Maria Kontopoulou, 
                 Efstratios Gallopoulos