Description 
This function contains the well known greedy algorithm for solving Set Cover problem (Chvátal, 1979), with two small modifications:
* In case of more than one possible choice at a certain step, the biggest set is chosen;
* Once the solution is found, we check the selected sets to find a better cover solution, removing a set if is a subset of the union of the other set.
If you use this code, please cite the article for which it was implemented:
F. Gori, G. Folino, M.S.M. Jetten, E. Marchiori
"MTR: Taxonomic annotation of short metagenomic reads using clustering at multiple taxonomic ranks", Bioinformatics 2010.
doi = 10.1093/bioinformatics/btq649

Additional information:
GREEDYSCP Greedy SCP algorithm.
[SolC,SolL] = GREEDYSCP(C, L) if C is an array, creates a cell array SolC that is a solution of Set Cover Problem defined by C, where C{i} = S_i, an input set made by some of the elements we want to cover; SolC is made by the cells of C selected by the algorithm. The elements that we want to cover are indicates by numbers from 1 to n, where n is the number of elements we want to cover; therefore, C{i} is a vector of integers between 1 and n.
If C is a logical or numerical array of n rows, where C(j,i) > 0 iff element j is contained in set S_i, the output SolC will be a logical array made by the column of log(C) corresponding to the solution
If a vector L of integer labels of the elements of C is provided, SolL contains the labels corresponding to SolC. Otherwise SolL contains the positions of elements of SolC in C. SolC and SolL elements are sorted in ascending order of SolL.
