[Cbc] Multiple Optimal Solutions

[Gabrielle A. Grun]

Hi John,

Are you really talking about multiple OPTIMAL answers or multiple intermediate solutions and       possibly one optimal solution?

Thanks.
  ----- Original Message ----- 
  From: John Forrest 
  To: cbc at list.coin-or.org 
  Sent: Wednesday, February 29, 2012 12:55 AM
  Subject: Re: [Cbc] Multiple Optimal Solutions


  Seeing the discussion of multiple solutions, I have made a few changes 
  to Cbc/trunk.

  I have modified Cbc/examples/driver4.cpp to show how you can print 
  solutions to preprocessed problem.  This example can be used in 
  Cbc/stable, but then user has to know if they are doing preprocessing as 
  the test may not be correct.  The values of the variables which are 
  still in the problem are printed correctly with the correct sequence 
  number (or name).  The values of variables which were preprocessed out 
  are not printed.  If the change below to Cbc is satisfactory then, at 
  greater computational expense, the complete solution could be printed.

  Cbc trunk has been altered so that postprocessing can be done several 
  times on different solutions.  As Cbc trunk normally uses Cgl/stable and 
  as stable code should not be modified too much, I have had to 
  temporarily make it a conditional compile.  So add -DKEEP_POSTPROCESS to 
  CXXDEFS in configure.  When Cgl/trunk migrates to stable, this will not 
  be necessary.

  Multiple solutions can now be printed or printed to file from the 
  executable.  There is a new integer parameter maxSolutions and a new 
  command nextB(estsolution) which acts like "solution", but works on the 
  second best solution and then moves all others up.  The best solution is 
  never touched.  So -

  cbc ...... -solve -solution best.sol -nextbest 2.sol -nextbest 3.sol 
  -solution best2.sol

  would put the best solution to best.sol and best2.sol while the second 
  best goes to 2.sol and the third best to 3.sol.  There is no action if 
  no solution.

  This was all a quick fix - I hope it helps.

  John Forrest
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