Release notes for GCG 2.0

GCG 2.0.1

features

• decomposition and pricing problems are permuted when the permutation seed is set
• progress in dual bound is now displayed while solving the root node
• pricing solvers can be enabled or disabled via parameter
• display blocks found for decomposition in statistics
• new boundtype for fixed original variables due to branching
• use new GCG column structure instead SCIP solution structure in pricing

code cleanup

• simplify code in generic branching
• structure of method branchVar()

bug fixes

• fix bugs concerning stabilization
• disable stabilization when linking variables or variables belonging to no block are present
• CPLEX pricing solver is disabled as it is incompatible with generic branching
• fix memory issues
• fix bound propagation bugs
• fix bug in knapsack solver
• delete constraints added at presolving after the root node
• check feasibility of current solution in original problem if this fails in the transformed problem
• fix wrong aggregation when using bliss
• print warnings when pricing is aborted
• fix translation of original solution to master problem when pricing problems are aggregated
• better handling of infinite objective values in pricing

GCG 2.0

features

• GCG can now automatically create a decomposition to solve the LP with empty pricing problems. See the cons/decomp/createbasicdecomp parameter
• GCG can aggregate pricing problems using bliss which enables us to aggregate more pricing problems
• GCG can solve pricing problems in parallel
• GCG uses dual variable smoothing to stabilize dual values
• GCG can branch on integer aggregated problems using Vanderbeck's general branching rule
• GCG can solve integer knapsack problems as a dynamic program
• GCG features additional detectors which are able to detect significantly more structures such as staircase structures and problems that can be aggregated
• improved heuristics
• copy solutions from original problem to master problem
• improved handling of compile flags changes such as an automatic recompilation if, e.g., USRFLAGS change
• new solver for pricing problems that uses CPLEX to solve the MIP (enabled if LPS=cpx)

code cleanup

• moved some detection methods to a more global scope to make them reusable
• added testing framework to do regression testing (uses google test)
• extracted graph methods for reuse
• branching is now done in the master problem
• remove code that was never called
• Rename methods in order to state their intention
• provide a gcg.h file to easily use the most common methods

bug fixes

• memory allocation bugs
• bound change propagation fixes
• corrected copyright
• fixed a lot of code checker issues
• use an event handler to disable the master display
• override PARASCIP=true if OPENMP=true
• correct decomp documentation and simplify decomposition interfaces