@techreport{TR-IC-97-22,
  number = {IC-97-22},
  author = {de Souza, C. C. and Wolsey, L. A.},
  title = {Scheduling Projects with Labour Constraints},
  month = {November},
  year = {1997}, 
  institution = {Institute of Computing, University of Campinas},
  note = {In English, 17 pages.
    \par\selectlanguage{english}\textbf{Abstract}
      In this paper we consider a labour constrained scheduling problem
      which is a simplification of a practical problem arising in the
      industry.  Jobs are subject to precedence constraints and have
      specified processing times.  Moreover, for each job the labour
      requirement varies as the job is processed. Given the amount of
      labour available in each period, the problem is to finish all the
      jobs as soon as possible (minimise {\em makespan}, subject to the
      precedence and labour constraints). Several Integer Programming (IP)
      formulations for this problem are discussed and valid inequalities
      for these different models are introduced. We point out to the major
      drawbacks in using the IP approach which are essentially due to the
      weakness of the lower bound relaxations.  However, we report
      computational experiments showing how IP can be used to provide good
      feasible solutions and we indicate directions for further
      investigations which may turn IP techniques an interesting tool for
      solving such a problem.
  }
}