Changeset 1892 for trunk/Cbc/README
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 Apr 8, 2013 6:09:19 AM (7 years ago)
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trunk/Cbc/README
r1884 r1892 71 71 "On the safety of Gomory cut generators" 72 72 http://faculty.sutd.edu.sg/~nannicini/index.php?page=publications 73 74 8. 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). 73 77 74 8.Allow initialization of random seed by user. Pseudorandom numbers are used in Cbc and Clp. In Clp they78 9. Allow initialization of random seed by user. Pseudorandom numbers are used in Cbc and Clp. In Clp they 75 79 are used to break ties in degenerate problems, while in Cbc heuristics such as the Feasibility Pump use them 76 80 to decide whether to round up or down. So if a different pseudorandom seed is given to Clp then you may get … … 79 83 for initial seed. 80 84 81 9. Building on this idea Andrea Lodi, Matteo Fischetti, Michele Monaci, Domenico Salvagninand Andrea Tramontani82 suggest that this idea be beimproved by running at the root node with multiple copies of solver, each85 10. 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 83 87 with its own different seed and then passing in the solutions and cuts so that the main solver has a richer 84 set of solutions and possibly stronger cuts. This is switched on by setting multipleRootPasses. These can also88 set of solutions and possibly stronger cuts. This is switched on by setting multipleRootPasses. These can also 85 89 be done in parallel. 86 90 87 10. Few changes to presolve for special variables and badly scaled problems (in CoinUtils). 88 89 11. New option extraVariables <number> which switches on a trivial reformulation to group variables with same cost together. 90 91 11. Few changes to presolve for special variables and badly scaled problems (in CoinUtils). 92 93 12. New option extraVariables <number> which switches on a trivial reformulation that introduces extra integer variables 94 to group together variables with same cost. 95 96 13. 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). 91 99 92 100 Release 2.7.8:
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