sifselect - selects a set of SIF problems
"n" no objective function
"c" constant objective function
"l" linear objective function
"q" quadratic objective function
"s" sum of squares objective function
"o" more general objective function
"u" no constraints
"x" constraints as fixed variables
"b" bound constraints
"n" constraints represented by adjacency matrix
"l" linear constraints
"q" quadratic constraints
"o" more general constraints
"r" problem is regular
"i" problem is irregular
sifselect(get_sif_path()+'sif/CLASSF.DB',['q','u','r])