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  • stable/2.8/Cbc/README

    r1804 r1902  
    2626==========
    2727
     28Release 2.8.0:
     29
     301. Introduced new secondaryStatus 8 to indicate that solving stopped due to an iteration limit.
     31
     322. Solution pool is now accessible via the command line and the CbcMain* interface.
     33
     343. New mipstart option to read an initial feasible solution from a file. Only values for discrete
     35   variables need to be provided.
     36
     374. Added Proximity Search heuristic by Fischetti and Monaci (off by default):
     38   The simplest way to switch it on using stand-alone version is "-proximity on".
     39
     40   Proximity Search is the new "No-Neighborhood Search" 0-1 MIP refinement heuristic recently proposed by
     41   Fischetti and Monaci (2012). The idea is to define a sub-MIP without additional constraints but with a
     42   modified objective function intended to attract the search in the proximity of the incumbent. The approach
     43   works well for 0-1 MIPs whose solution landscape is not too irregular (meaning the there is reasonable
     44   probability of finding an improved solution by flipping a small number of binary variables), in particular
     45   when it is applied to the first heuristic solutions found at the root node.
     46   
     475. An implementation of Zero-Half-Cuts by Alberto Caprara is now available.
     48   By default, these cuts are off.  To use add to your command line -zerohalfCuts root (or other options) or just -zero.
     49   So far, they may help only on a small subset of problems and may need some tuning.
     50
     51   The implementation of these cuts is described in
     52   G. Andreello, A. Caprara, and M. Fischetti
     53   "Embedding Cuts in a Branch and Cut Framework: a Computational Study with {0,1/2}-Cuts"
     54   INFORMS Journal on Computing 19(2), 229-238, 2007
     55   http://dx.doi.org/10.1287/ijoc.1050.0162
     56
     576. An alternative implementation of a reduce and split cut generator by Giacomo Nannicini is now available.
     58   By default, these cuts are off.  To use add to your command line -reduce2AndSplitCuts root (or other options).
     59
     60   The implementation of these cuts is described in
     61   G. Cornuejols and G. Nannicini
     62   "Practical strategies for generating rank-1 split cuts in mixed-integer linear programming"
     63   Mathematical Programming Computation 3(4), 281-318, 2011
     64   http://dx.doi.org/10.1007/s12532-011-0028-6
     65
     667. An alternative robust implementation of a Gomory cut generator by Giacomo Nannicini is now available.
     67   By default, these cuts are off.  To use add to your command line -GMI root (or other options).
     68
     69   The implementation of these cuts is described in
     70   G. Cornuejols, F. Margot, and G. Nannicini
     71   "On the safety of Gomory cut generators"
     72   http://faculty.sutd.edu.sg/~nannicini/index.php?page=publications
     73
     748. To encourage the use of some of the more exotic/expensive cut generators a parameter -slowcutpasses has been added.
     75   The idea is that the code does these cuts just a few times - less than the more usual cuts.  The default is 10.
     76   The cut generators identified by "may be slow" at present are just Lift and project and ReduceAndSplit (both versions).
     77   
     789. Allow initialization of random seed by user.  Pseudo-random numbers are used in Cbc and Clp.  In Clp they
     79   are used to break ties in degenerate problems, while in Cbc heuristics such as the Feasibility Pump use them   
     80   to decide whether to round up or down.  So if a different pseudo-random seed is given to Clp then you may get
     81   a different continuous optimum and so different cuts and heuristic solutions. This can be switched on by
     82   setting randomSeed for Clp and/or randomCbcSeed for Cbc.  The special value of 0 tells code to use time of day
     83   for initial seed.
     84   
     8510. Building on this idea, Andrea Lodi, Matteo Fischetti, Michele Monaci, Domenico Salvagnin, Yuji Shinano, and Andrea Tramontani
     86   suggest that this idea be improved by running at the root node with multiple copies of solver, each
     87   with its own different seed and then passing in the solutions and cuts so that the main solver has a richer
     88   set of solutions and possibly stronger cuts.  This is switched on by setting -multipleRootPasses.  These can also
     89   be done in parallel.
     90 
     9111. Few changes to presolve for special variables and badly scaled problems (in CoinUtils).
     92
     9312. New option -extraVariables <number> which switches on a trivial re-formulation that introduces extra integer variables
     94    to group together variables with same cost.
     95
     9613. For some problems, cut generators and general branching work better if the problem would be infeasible if the cost is too high.
     97    If the new option -constraintFromCutoff is set, the objective function is added as a constraint which rhs is set to the current
     98    cutoff value (objective value of best known solution).
     99
    28100Release 2.7.8:
    29101   Look at https://projects.coin-or.org/Cbc/changeset?old_path=%2Freleases%2F2.7.7&new_path=%2Freleases%2F2.7.8 to see all changes.
     
    102174
    1031753. Support for BuildTools version 0.7 to incorporate recent enhancements,
    104    including proper library versioning in Linux, prohibiting installation of
    105    private headers, etc.
     176including proper library versioning in Linux, prohibiting installation of
     177private headers, etc.
    106178
    1071794. Updated externals to new stable versions of dependent projects.
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