@techreport{TR-IC-03-12,
  number = {IC-03-12},
  author = {E. C. Xavier and F. K. Miyazawa},
  title = {Approximation Schemes for a
           Class-Constrained Knapsack Problem},
  month = {April},
  year = {2003}, 
  institution = {Institute of Computing, University of Campinas},
  note = {In English, 15 pages.
    \par\selectlanguage{english}\textbf{Abstract}
       We  present approximation  algorithms  for a  class-constrained
       version of the knapsack problem: Given an integer $K$, a set of
       items  $S$, each  item with  value, size  and a  class,  find a
       subset  of $S$  of  maximum  total value  such  that items  are
       grouped in compartments.  Each compartment must have only items
       of  one   class  and  must  be  separated   by  the  subsequent
       compartment  by a  wall  division of  size  $d$. Moreover,  two
       subsequent  wall divisions  must stay  a distance  of  at least
       $d_{\min}$  and at  most  $d_{\max}$. The  total  size used  by
       compartments and by  wall divisions must be at  most $K$.  This
       problem have practical applications on cutting-stock problems.
  }
}