COMPUTE_SCAT - computes the cluster selection criterion value 
  of PDDP
    SCAT=COMPUTE_SCAT(A, C) returns the square of the frobenius 
    norm of A-C*ones(1, size(A, 2)).
 
  Copyright 2011 Dimitrios Zeimpekis, Eugenia Maria Kontopoulou, 
                 Efstratios Gallopoulos