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CHANGELOG
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@page RN10 Release notes for SCIP 10
@section RN1000 SCIP 10.0.0
***************************
Features
--------
- added new fields in history to store ancestral pseudo cost updates, used in the pseudo costs branching rule to compute discounted pseudo costs.
- copy variable data pointer if no copy routine was supplied.
- added more techniques to handle reflection symmetries, in particular, for orbitopes with column reflections and matrices whose rows and columns can be permuted by a symmetry
- Dejavu can be used to compute symmetries; the source code is shipped with SCIP and incorporates sassy.
- implemented symmetry detection callbacks for cons_disjunction and cons_superindicator
- detailed information about applied symmetry handling techniques can be printed to the terminal
- added a new separator sepa_multilinear to generate flower cuts from AND constraints nonlinear product expressions.
- added functionality to deal with hypergraphs by means of efficient access to vertices, edges and intersections edges.
- added support for (transposed) network matrix detection in pub_network.h
- added a new presolver presol_implint which detects implied integral variables by detecting (transposed) network submatrices in the problem. For now, this plugin is disabled by default.
- added new plugin type for finding irreducible infeasible subsystems (IIS). Users can now include their own IIS algorithms. Basic addition and deletion based algorithm implemented in iisfinder_greedy.
- added a new data structure SCIP_DATATREE that holds serializable data and a method to export to a JSON file
- added ability to collect statistics from tables in a SCIP_DATATREE and write out as JSON file;
dialog write statistics now writes a JSON file if name of file to write ends with .json
- improve memory usage by introducing different constraint handlers for full orbitopes and packing/partitioning orbitopes
- the linking master variables for each Benders' decomposition subproblem are now stored. These can be accessed for the
generation of cut and setting up the subproblems.
- adds objective types for Benders' decomposition; the choice is to sum the subproblems objectives (classical
approach) or to use the maximum of the subproblems objectives
Performance improvements
------------------------
- reimplemented SCIPvarGetActiveRepresentatives() by using dense arrays to avoid repeated resorting.
Examples and applications
-------------------------
- Coloring: new parameter branching/coloring/strategy to choose the least/most fractional variable for branching
Interface changes
-----------------
### Deprecations
- The variable type \ref SCIP_VARTYPE_IMPLINT is deprecated in favor of a new enum \ref SCIP_IMPLINTTYPE that indicates if a
variable is implied integral, independent of the variable type.
The problem variable arrays is still sorted as:
```
(0) | binary | integer | implied integral | continuous | (nvars),
```
where the implied integral subsection is now subdivided into 3 parts (left to right):
```
| binary implied integral | integer implied integral | continuous implied integral |
```
SCIP 10 still supports using SCIP_VARTYPE_IMPLINT for backward compatibility, see SCIPcreateVar() and SCIPchgVarType() for more details.
SCIP 11 will remove SCIP_VARTYPE_IMPLINT.
### New and changed callbacks
- added a new callback TABLE_COLLECT for the table plugin that collects the data for the specific statistics table in a SCIP_DATATREE object
- for a table plugin, only one of the callbacks TABLE_COLLECT or TABLE_OUTPUT needs to be implemented, but implementing both is preferred;
if TABLE_OUTPUT is omitted, then SCIP tries to print a table from the data given by TABLE_COLLECT
- the event SCIP_EVENTTYPE_TYPECHANGED is no longer generated if a variable becomes implied integral
- new event SCIP_EVENTTYPE_IMPLTYPECHANGED is generated if a variable is declared implied integral, this event is included in the set SCIP_EVENTTYPE_VARCHANGED
- the callback SCIP_DECL_EXPRINTEGRALITY, which returns the integrality of an expression, had its fourth argument change from SCIP_Bool* to SCIP_IMPLINTTYPE*, to represent implied integrality in nonlinear expressions, that is an implied integral type of an auxiliary variable if the expression were assigned to it
### Deleted and changed API methods
- SCIPgetProbvarLinearSum: remove parameter mergemultiples, which is now automatically true with the new implementation of SCIPvarGetActiveRepresentatives.
- SCIPcreateRow*(), SCIPaddVarToRow(), SCIPaddVarsToRow(), SCIPaddVarsToRowSameCoef() can now only be called in the solving stage,
because otherwise the LP is not yet available and the row data is invalid.
- intvar removed from arguments for SCIPcreateConsPseudobooleanWithConss(), SCIPcreateConsPseudoboolean(), and SCIPcreateConsBasicPseudoboolean() due to dysfunctionality of non-linear objective reformulation with pseudoboolean constraint
- ndelconss added to arguments for SCIPcleanupConssLinear() and SCIPcleanupConssKnapsack() to directly delete empty redundant constraints before creating problem matrix
- copyiisfinders added to arguments for SCIPcopyPlugins() (16th position)
- SCIPcreateConsOrbitope() deleted two arguments and changed position of another argument
- deprecated SCIPsubversion(), will be removed
- SCIPvarCalcDistributionParameters(): argument impltype added (5th position)
- SCIPpermuteProb(): argument permuteimplvars has been replaced by new arguments permutebinimplvars, permuteintimplvars, and permutecontimplvars
- SCIPgetSolVarsData(): argument nimplvars has been replaced by new arguments nbinimplvars, nintimplvars, and ncontimplvars
- SCIPexprSetIntegrality(): set argument generalized from SCIP_Bool integral to SCIP_IMPLINTTYPE integrality (4th position)
- Temporarily for SCIP 10 only: Creating a variable SCIPcreateVar() with type SCIP_VARTYPE_IMPLINT creates a variable of type SCIP_VARTYPE_CONTINUOUS and implied integral type SCIP_IMPLINTTYPE_WEAK instead
- Temporarily for SCIP 10 only: SCIPchgVarType() converts a call with type SCIP_VARTYPE_IMPLINT into a call of SCIPchgVarImplType() with type SCIP_IMPLINTTYPE_WEAK
### New API functions
- SCIPhistoryUpdateAncPseudocost(), SCIPvarUpdateAncPseudocost() for updating the ancestral pseudo cost fields in variable history
- SCIPhistoryGetAncPseudocost(), SCIPhistoryGetAncPseudocostCount(), SCIPhistoryIsAncPseudocostEmpty(), SCIPgetVarAncPseudocostVal(),
SCIPvarGetAncPseudocost() for retrieving the values related to ancestral pseudo cost fields in variable history
- SCIPgetAvgDPseudocostScore(), SCIPgetVarDPseudocostScore() for computing the discounted pseudo cost scores using ancestral pseudo costs
- SCIPboundchgGetLPSolVal() for accessing the LP solution value in the branching data of the bound change
- SCIPclearSymgraph() and SCIPcopySymgraphAsSubgraph() to clear and copy as symmetry detection graph, respectively
- SCIPincludeSepaMultilinear() to include the new multilinear cut separator
- SCIPhypergraphCreate(), SCIPhypergraphClear(), SCIPhypergraphFree(), SCIPhypergraphAddVertex(), SCIPhypergraphAddEdge(), SCIPhypergraphIsValid() and SCIPhypergraphComputeVerticesEdges() for building and deleting hypergraphs, SCIPhypergraphComputeOverlaps(), SCIPhypergraphOverlapFind(), SCIPhypergraphIntersectEdges(), SCIPhypergraphComputeOverlapsEdges(), SCIPhypergraphComputeVerticesOverlaps(), SCIPhypergraphOverlapsDisjoint() to deal with pair-wise intersections of hyperedges, SCIPhypergraphIterInit(), SCIPhypergraphIterClear(), SCIPhypergraphIterStart(), SCIPhypergraphIterValid(), SCIPhypergraphIterNext(), SCIPhypergraphIterBase(), SCIPhypergraphIterAdjacent(), SCIPhypergraphIterMinVertex(), SCIPhypergraphIterOverlap() for iterating over adjacent edges, SCIPhypergraphHasVertexEdges() SCIPhypergraphHasOverlaps(), SCIPhypergraphHasOverlapsEdges(), SCIPhypergraphHasVertexOverlaps(), SCIPhypergraphGetNVertices(), SCIPhypergraphGetNEdges(), SCIPhypergraphBlkmem(), SCIPhypergraphGetNOverlaps(), SCIPhypergraphVertexData(), SCIPhypergraphEdgeData(), SCIPhypergraphEdgeSize(), SCIPhypergraphEdgeVertices(), SCIPhypergraphVertexEdgesFirst(), SCIPhypergraphVertexEdgesBeyond(), SCIPhypergraphVertexEdgesGetAtIndex(), SCIPhypergraphOverlapData(), SCIPhypergraphOverlapSize(), SCIPhypergraphOverlapVertices() SCIPhypergraphEdgesOverlapsFirst(), SCIPhypergraphEdgesOverlapsBeyond(), SCIPhypergraphEdgesOverlapsGetAtIndex(), SCIPhypergraphOverlapsEdgesFirst(), SCIPhypergraphOverlapsEdgesBeyond(), SCIPhypergraphOverlapsEdgesGetAtIndex(), SCIPhypergraphVertexOverlapsFirst(), SCIPhypergraphVertexOverlapsBeyond() and SCIPhypergraphVertexOverlapsGetAtIndex() to query information about vertices, edges and overlaps as well as their incidences.
- SCIPdebugClearSol() for clearing the debug solution
- Renamed XML functions to avoid name clash with libxml2 by adding "SCIP": SCIPxmlProcess(), SCIPxmlNewNode(), SCIPxmlNewAttr(), SCIPxmlAddAttr(), SCIPxmlAppendChild(), SCIPxmlFreeNode(), SCIPxmlShowNode(), SCIPxmlGetAttrval(), SCIPxmlFirstNode(), SCIPxmlNextNode(), SCIPxmlFindNode(), SCIPxmlFindNodeMaxdepth(), SCIPxmlNextSibl(), SCIPxmlPrevSibl(), SCIPxmlFirstChild(), SCIPxmlLastChild(), SCIPxmlGetName(), SCIPxmlGetLine(), SCIPxmlGetData(), SCIPxmlFindPcdata().
- SCIPincludePresolImplint() to include the new implied integral presolver
- SCIPnetmatdecCreate() and SCIPnetmatdecFree() for creating and deleting a network matrix decomposition. SCIPnetmatdecTryAddCol() and SCIPnetmatdecTryAddRow() are used to add columns and rows of the matrix to the decomposition. SCIPnetmatdecContainsRow() and SCIPnetmatdecContainsColumn() check if the decomposition contains the given row or columns. SCIPnetmatdecRemoveComponent() can remove connected components from the decomposition. SCIPnetmatdecCreateDiGraph() can be used to expose the underlying digraph. SCIPnetmatdecIsMinimal() and SCIPnetmatdecVerifyCycle() check if certain invariants of the decomposition are satisfied and are used in tests.
- SCIPfreeReaderdataCor(), SCIPfreeReaderdataTim() and SCIPfreeReaderdataSto() for freeing the data for the COR, TIM and
STO readers respectively. These readers are all used when reading an SMPS instance.
- SCIPdialogIsHidden(), SCIPdialogSetHidden() to determine whether a dialog should be hidden in help list
- added SCIPincludeIISfinder(), SCIPincludeIISfinderBasic(), SCIPsetIISfinderCopy(), SCIPsetIISfinderFree(), SCIPgenerateIIS(), SCIPfindIISfinder(), SCIPgetIISfinders(), SCIPgetNIISfinders(), SCIPsetIISfinderPriority(), SCIPgetIIS()
- added SCIPiisfinderGetName(), SCIPiisfinderGetData(), SCIPiisfinderGetDesc(), SCIPiisfinderGetPriority(), SCIPiisfinderSetData(), SCIPiisfinderGetTime(), SCIPiisfinderInfoMessage(), SCIPiisGetTime(), SCIPiisIsSubscipInfeasible(), SCIPiisIsSubscipIrreducible(), SCIPiisGetNNodes(), SCIPiisSetSubscipInfeasible(), SCIPiisSetSubscipIrreducible(), SCIPiisAddNNodes(), SCIPiisGetRandnumgen(), SCIPiisGetSubscip()
- functions to create, modify, and free SCIP_DATATREE objects and to print as JSON or table (see pub_datatree.h and scip_datatree.h)
- SCIPcollect*Statistics() for every SCIPprint*Statistics() in scip_solvingstats.h
- SCIPprintStatisticsJson() to output a JSON string of the table statistics data
- SCIPstatusName() to get a string representation of SCIP_STATUS
- SCIPbendersGetSubproblemMasterVars(), SCIPbendersGetNSubproblemMasterVars(), SCIPbendersGetSubproblemMasterVarsData()
are available to get the linking master variables for each subproblem and details about the number of binary and integer.
- SCIPsetBendersObjectiveType() for setting the objective type for the aggregation of the Benders' decompostion
subproblems
- SCIPbendersGetObjectiveType() for returning the objective type for the aggregation of the Benders' decomposition
subproblems
- SCIPbenderGetMasterAuxiliaryVar() returns the master auxiliary variable
- added SCIPcreateVarImpl() and SCIPcreateObjVarImpl(), which behave identically to SCIPcreateVar() and SCIPcreateObjVar(), respectively, but have an additional argument for the new implied integral type flag (8th position)
- added SCIPchgVarImplType(), SCIPvarGetImplType(), SCIPvarIsImpliedIntegral() to control and query implied integrality
- added SCIPgetNBinImplVars(), SCIPgetNIntImplVars(), SCIPgetNContImplVars() to query the number of implied integral variables of every type; note that SCIPgetNBinVars(), SCIPgetNIntVars(), and SCIPgetNContVars() no longer include the implied integral variables in their counts
- added SCIPcolIsImpliedIntegral()
- added SCIPvarsCountTypes() to determine the variable type count distribution for an array of variables
- added SCIPeventGetOldImplType() and SCIPeventGetNewImplType() to query the new event SCIP_EVENTTYPE_IMPLTYPECHANGED
- added SCIPexprGetIntegrality(), which in addition to the existing function SCIPexprIsIntegral() provides information about the presence of weakly implied integral variables
### Changes in preprocessor macros
- removed `#define` of `strcasecmp` and `strncasecmp` (in case of Windows builds) in scip/def.h;
use SCIPstr(n)casecmp() (scip/pub_misc.h) instead
- SCIPincludeConshdlrOrbitopePP(), SCIPcreateConsOrbitopePP(), SCIPcreateConsBasicOrbitopePP(), SCIPincludeConshdlrOrbitopeFull(), SCIPcreateConsOrbitopeFull(), SCIPcreateConsBasicOrbitopeFull()
- SCIP_VERSION_SUB and SCIP_SUBVERSION are deprecated
- removed SCIP_VARTYPE_IMPLINT_CHAR
### Command line interface
- help <command> now allows to display information on specific command.
- allow to hide certain commands in the help list
- add the (hidden) command "exit" to exit SCIP.
- Add iis option to create an infeasible subsystem
- Add write/iis option to write out the infeasible subsystem to file
- Add display/iis option to write out the infeasible subsystem to console
### Interfaces to external software
### Changed parameters
- heuristics/scheduler/heurtimelimit removed to avoid indeterministic behavior of scheduler heuristic, uses main time limit instead
- removed parameters "constraints/orbitope/checkpporbitope", "constraints/orbitope/sepafullorbitope", "constraints/orbitope/forceconscopy", which became superfluous
- removed reading/gmsreader/signpower
### New parameters
- branching/pscost/discountfactor, branching/relpscost/discountfactor as the discount factor for ancestral pseudo costs in pscost and relpscost branching rules
- branching/discountedpscost to enable/disable recording ancestral pseudo costs
- new parameter "propagating/symmetry/handlesignedorbitopes" to control whether special symmetry handling techniques for orbitopes whose columns can be (partially) reflected shall be applied
- new parameter "propagating/symmetry/usesimplesgncomp" to control whether symmetry components all of whose variables are simultaneously reflected by a symmetry shall be handled by a special inequality
- new parameter "propagating/symmetry/dispsyminfo" to control whether information about which symmetry handling methods are applied are printed
- new parameter "presolving/implint/columnrowratio" indicates the ratio of rows/columns where the row-wise network matrix detection algorithm is used instead of the column-wise network matrix detection algorithm
- new parameter "presolving/implint/numericslimit" determines the limit for absolute integral coefficients beyond which the corresponding rows and variables are excluded from implied integrality detection
- iis/minimal, iis/nodes, iis/removedbounds, iis/removeunusedvars, iis/silent, iis/stopafterone, iis/time, iis/greedy/additive, iis/greedy/conservative, iis/greedy/delafteradd, iis/greedy/dynamicreordering, iis/greedy/maxbatchsize, iis/greedy/maxrelbatchsize, iis/greedy/nodelimperiter, iis/greedy/priority, iis/greedy/timelimperiter
- new parameters "constraints/orbitope_full/forceconscopy" and "constraints/orbitope_pp/forceconscopy" to control whether non-model constraints of type full orbitope and packing/partitioning orbitope are copied to sub-SCIPs, respectively
- new parameter "write/implintlevel" to control if integrality constraints should be written for implied integral variables (regarded by cip, mps, lp, rlp, pip, fzn, and gms writers)
### Data structures
- added structs SCIP_IISFINDER, SCIP_IISFINDERDATA, SCIP_IIS
- added struct SCIP_DATATREE to model generic serializable data; new enum SCIP_DATATREE_VALUETYPE
Deleted files
-------------
Testing
-------
Build system
------------
- changed the default for TPI to tny
### Makefile
### Cmake
- increased minimal required cmake version to 3.11
- removed automatic download and build of Bliss during cmake configuration when -DSYM=(s)bliss;
please build and install from https://github.com/scipopt/bliss before and specify -DBLISS_DIR
Fixed bugs
----------
- fixed bug related to unreleased data for the Benders' decomposition framework. When reading an SMPS file and applying
Benders' decomposition, data is created that was not correctly released. Also, data within the Benders' decomposition
framework was not appropriately reset. The data is now released/reset as expected.
Miscellaneous
-------------
- We now use sassy as shipped with dejavu.
- add objective offset instead of objective offset variable in cip reader
- updated ampl/mp to v4.0.0
- removed 4th number in SCIP version; new format is major.minor.patch
Known bugs
----------
@page RN9 Release notes for SCIP 9
@section RN930 SCIP 9.3.0
*************************
Features
--------
- simplify expressions of nonlinear constraints in MPS and LP writing to increase chance that they are recognized as quadratic
Performance improvements
------------------------
Examples and applications
-------------------------
Interface changes
-----------------
### New and changed callbacks
### New API functions
- SCIPdisplaySymmetryGenerators() and SCIPdialogExecDisplaySymmetry() to display generators of symmetry group
### Command line interface
### Interfaces to external software
### Changed parameters
### New parameters
### Data structures
Fixed bugs
----------
Miscellaneous
-------------
- updated description of paramater misc/usesymmetry
@section RN922 SCIP 9.2.2
*************************
Fixed bugs
----------
- fixed definition of slack variables of >= constraints and ranged rows in LP interface to Gurobi (lpi_grb.c)
- free memory leaking singleton arrays for ignored variables in SCIPapplyHeurDualval()
- use epsilon tolerance for bound implications of dual substitutions in dualPresolve() of cons_linear.c
Build system
------------
### Cmake
- allow to set HIGHS_DIR via -D flag as well
### Makefile
Miscellaneous
-------------
@section RN921 SCIP 9.2.1
*************************
Fixed bugs
----------
- apply same feasibility definition in PaPILO as in SCIP to avoid numerical inconsistencies
- check variable cancellation in SCIPvarAddVlb() and SCIPvarAddVub() to avert wrong infeasibility
- SCIPfreeReoptSolve() now also clears partial solutions
- fixed bug in calculation of "fractionality score" for spatial branching candidates in cons_nonlinear
- fixed bug with installing symmetry dialog in sub-SCIPs
- added copy callbacks for presolvers dualagg and redvub, branching rules lookahead and cloud, primal heuristics dualval and repair, propagator nlobbt, and separators gauge and convexproj
- respect maximal separation rounds setting by running remaining delayed separators in last round
- replace terms consistently in applyFixings() of cons_linear to handle infinite aggregations
- fixed bug with SOS2 constraints of size that avoided a correct enforcing
Build system
------------
### Cmake
- fix SCIP Optimization Suite build with -DSYM=(s)bliss and bliss being downloaded and built during configuration by cmake
- fix use of a bliss cmake installation (from https://github.com/scipopt/bliss) specified via BLISS_DIR if -DSYM=(s)bliss
### Makefile
- the check/solchecker build can now use also GMP installations by Homebrew on macOS/arm64
Miscellaneous
-------------
- the output precision for writing CIP/OPB files has been increased at several places for nonlinear constraints
- the solchecker tool now also supports SCIP solutions without unknown or infinite values
- generate an error if the same linear constraint is used by several indicator constraints
@section RN920 SCIP 9.2.0
*************************
Features
--------
- added check for absolute and relative gap limits at end of synchronization in concurrent solving mode, in order to terminate earlier;
note that if the concurrent solve is stopped due to a gap limit, the "winner" solver will have an interrupted solution status and
its primal and dual bounds may not be the best possible ones (use SCIPgetConcurrentPrimalbound() and SCIPgetConcurrentDualbound() instead)
- parse pseudoboolean constraint from CIP format (and add linear-"and"-reformulation)
Performance improvements
------------------------
- reoptimization now also stores propagations from propagators if reoptimization/saveconsprop is enabled;
the parameter will be renamed to reoptimization/saveprop in a next major release
- imposed stricter limits on the size of disconnected components which may be solved separately during presolve
- use individual slack variables also for constraints indicated by a common binary variable to use tighter formulation by default
- when computing symmetries using Nauty, iteration limits are now available to terminate Nauty early
Fixed bugs
----------
- Benders' decomposition subproblems that are always infeasible are correctly handled and the complete problem is declared infeasible
- skip linear constraint propagation if the residual activity bound cancels the side precision
- correct bound tracking to make the evaluation of primal-dual-integrals work
- skip aggregations on fixed variables in milp presolver to avoid errors for earlier versions of PaPILO
- use indices of negation counterparts and accept fixings when ordering and-resultants of pseudoboolean constraints
- update locks on model variables before removing pseudoboolean constraints in presolve
- reformulate soft pseudoboolean constraints with linear constraints if the indicator decomposition is disabled
- add workaround for recent HiGHS versions resetting the model status when changing the presolve option after a solve
- avoid hashmap key error in removal of doubletons and singletons in dual presolve of setppc constraints by updating constraints and corresponding hashmaps after each multi-aggregation
Interface changes
-----------------
### New API functions
- added SCIPtpiIsAvailable() to check whether a working task processing interface is available (TPI != none)
- added SCIPtpiGetLibraryName() and SCIPtpiGetLibraryDesc()
- SCIPdelCons() can now also be called in SCIP_STAGE_TRANSFORMED
- added SCIPstrcasecmp() and SCIPstrncasecmp() for case-insensitive string comparison
- added SCIPbendersSubproblemsAreInfeasible() to return if at least one subproblem has been identified as being
infeasible prior to performing any variable fixing
### New parameters
- presolving/milp/abortfacexhaustive to control the abort threshold for exhaustive presolving in PAPILO
- presolving/milp/abortfacmedium to control the abort threshold for medium presolving in PAPILO
- presolving/milp/abortfacfast to control the abort threshold for fast presolving in PAPILO
- constraints/components/maxcompweight to determine the maximum weight for a disconnected component that is solved during presolve
- constraints/components/contfactor counts the contributing factor of a single continuous variables with respect to the weight limit specified by constraints/components/maxcompweight
- constraints/indicator/usesameslackvar to decide whether the same slack variable should be used for indicators constraints with common binary variable
- propagating/symmetry/nautymaxncells and propagating/symmetry/nautymaxnnodes to set iteration limits in Nauty (only available if build with SYM=nauty or SYM=snauty)
### Changed parameters
- presolving/milp/threads is now only available if PaPILO is built with TBB
- changed default of numerics/recomputefac to 1e+6 to aim at relative epsilon precision
Build system
------------
### Cmake
- attempted to fix detection of CPLEX library on macOS and Windows systems
Testing
-------
- added parameter FILTER for tests/Makefile to run only tests with a specific pattern (ctest with -R FILTER)
Miscellaneous
-------------
- adjusted Gurobi interface for Gurobi 12
- reordered events: BESTSOLFOUND/NODE_FEASIBLE are now processed before the nodes are cut off and before NODE_DELETE events are processed
- removed `#define` of `getcwd` (in case of Windows builds) in scip/def.h
- the `#define` of `strcasecmp` and `strncasecmp` (in case of Windows builds) in scip/def.h will be removed with SCIP 10;
use `SCIPstr(n)casecmp()` (scip/pub_misc.h) instead
@section RN911 SCIP 9.1.1
*************************
Fixed bugs
----------
- fix bug in separator aggregation that caused incorrect terminations when for an integral objective the objective limit was set to a fractional value
- fix bug in memory management of doublelex matrices where indices were set beyond array bounds
- store relevance flags in consdataTightenCoefs() of cons_linear.c to avoid dropping variables unintentionally due to numerical changes
- fix possible segmentation fault when resetting local and global bounds of original variables after abnormal termination
- compare coefficient scales to detect parallelism to avoid integral relaxations in detectRedundantConstraints() of cons_linear.c
- remove coefficient information from linear constraint hashes in order to compare keys with tolerances
- fixed NULL pointer dereference in SCIPtpiGetNumThreads() of TinyCThread interface if called before SCIPtpiInit(); now returns 0 in this case
- calling SCIPsolveConcurrent() when SCIP was compiled without a TPI now results in a plugin-not-found error
- fixed LPI status functions of lpi_cpx if the barrier is called
- check cuts for redundancy after scaling in cutTightenCoefs() and cutTightenCoefsQuad() of cuts.c
- maintain definition of artificial integral variables in xor constraints to avoid invalidation of conflict constraints
- free childless nodes only after the deactivation of the old focus path in treeSwitchPath() of tree.c
- only normalize rows for column norm evaluations in shift-and-propagate heuristic to avoid unscaled violations
- expression handler for absolute value computes now also a cut when one of the bounds is infinite as long as the sign of the argument is known
- check for more data to be freed before modifying nonlinear constraints in SCIPaddExprNonlinear()
- allow for terms with zero coefficients when checking sum in SCIPexprCheckQuadratic()
- do not abort writing of constraints to lp/pip files (and forget to free buffer memory) when encountering unsupported nonlinear constraint
- fixed that strings with names and descriptions of the LPI's were not null-terminated
- fixed decision on when to enforce nonlinear constraints on relaxation solutions if integer variables are present
- fixed reading of very long lines (>78000 characters) in FlatZinc reader
- fixed write of strings with at least 1024 characters when compiling with MSVS 2015 (14.0) or later (still an issue with earlier MSVS, which will not be fixed)
- keep epsilon coefficients in applyFixings() of cons_linear.c until multiples are merged to avoid loss of relevant contributions
- fixed that some variable type changes were not accounted correctly in presolve of linear constraints
- fix constraint sorting in setpp-orbitope upgrade in symmetry code
- fixed that SCIPnodeGetConsProps() also counted bound changes from propagators
- use original and-constraints of an untransformed pseudoboolean constraint when copying original problems to avert segmentation faults
- sort and-constraints of a pseudoboolean constraint with respect to the resultant problem indices to avoid shuffled copies
- treat pseudoboolean constraints as nonlinear constraints in OPB reader to prevent duplication mistakes
Examples and applications
-------------------------
- in example Binpacking implement Farkas pricing for packings because branching can actually lead to infeasible restricted master LPs
Testing
-------
- allow unknown parameters to let tests pass if only optional dependencies are missing
Build system
------------
### Cmake
- fixed compilation and linking with HiGHS; to use HiGHS, cmake now requires to specify the directory containing the `highs-config.cmake` file via `-DHIGHS_DIR`
- extended identification of Ipopt library on Windows to also look for ipopt.dll.lib, as this is used since Ipopt 3.13.0 (2019)
@section RN910 SCIP 9.1.0
*************************
Features
--------
- added constraint handler that checks and enforces bounds on original variables which have been fixed or aggregated in the transformed problem
- allow for implicit integer variables in xor constraints
- implemented symmetry detection callbacks for pseudoboolean constraints
- added option to consider enforcement of nonlinear constraints (including spatial branching) before integrality has been enforced
Fixed bugs
----------
- make sure that, in dual proof analysis, upgraded constraints can report their number of variables
- check knapsack constraints as linear constraints to avoid violations based on implicit integrality
- make sure that symmetry detection callbacks report success
- make arithmetics in cuts.c more robust to avoid invalid scg cuts due to numerical rounding sensitivity
- allow to copy pseudoboolean constraints even if no AND constraints are present in order to avoid a warning
- set value for variable that is introduced to reformulate nonlinear objective function when reading .nl files with initial solution
- fixed that multi-aggregations from PaPILO were accepted without ensuring that their bounds hold
Examples and applications
-------------------------
- TSP: removed `gzstream.h/hpp` and parse gzipped files differently
Interface changes
-----------------
### New callbacks
- SCIP_DECL_NLHDLRENFO takes additional parameter branchcandonly to indicate whether only branching candidates should be registered,
without looking for cuts or boundchanges
### New API functions
- new function SCIPgetExprActivityNonlinear() to get activity of nonlinear constraint
- new function SCIPincludeConshdlrFixedvar() to include new constraint handler that checks bounds on fixed original variables
### New parameters
- limits/primal to terminate the solve as soon as the primal bound is at least as good as this value, same as limits/objectivestop (deprecated)
- limits/dual to terminate the solve as soon as the dual bound is at least as good as this value
- presolving/milp/internalmaxrounds to control the maximal rounds for each call of the milp presolver (PaPILO)
- constraints/fixedvar/* to control the new constraint handler that checks bounds on fixed original variables
- constraints/nonlinear/branching/mixfractional to specify minimal average pseudo cost count for discrete variables
at which to start considering spatial branching before branching on fractional integer variables
(default infinity means that integrality is always enforced before nonlinear constraints)
- constraints/nonlinear/branching/fracweight to specify weight of fractionality of integer variables in spatial branching
### New data structures
- enum SCIP_Status has been extended by SCIP_STATUS_PRIMALLIMIT and SCIP_STATUS_DUALLIMIT to indicate termination at limits/primal and limits/dual respectively
Build system
------------
- new option SYM=dejavu to choose Dejavu for computing symmetries
- changed the default symmetry computation package from sassy+bliss to sassy+nauty
- bliss source is no longer included in the source tree, but can be linked as external library (https://github.com/ds4dm/Bliss)
- cmake now automatically downloads and installs the latest release version of SoPlex from GitHub if it is not found directly
Miscellaneous
-------------
- updated nauty to version 2.8.8
@section RN901 SCIP 9.0.1
*************************
Fixed bugs
----------
- fixed bug in detection of double lex matrices due to wrong memory allocation
- fixed bug where parameter `limits/objectivestop` was copied to subscips in plugins which have different objectives
- in count mode respect empty solution when problem is solved in presolving
- fixed that SCIP may have tried to pass a negative random seed to an LP solver
- fixed bug where conflict analysis in strong branching tried to analyze an unsuccessful LP solve
- enable parameter limits/restarts by allowing to reach the restart limit in restartAllowed()
- handle normalizing linear constraints in presolving with more caution to avoid numerical difficulties for integer variables with large coefficients
- use quad precision to calculate residual activity bounds to reduce numerical errors for large variable bounds in cons_linear.c
- in SCIPsolveProbingLP() when objective has been changed do not return cutoff due to exceeding the cutoff bound
- set probing LP to be a relaxation only when objective has not been changed
- declare contradicting infinities in getMinActivity() and getMaxActivity() as non-tight
- reject farkas solution with large values to bound magnification of errors in SCIPgetFarkasProof()
- if all variables are fixed, apply relative feasibility tolerance to avoid invalid infeasibility in applyFixings() of cons_linear.c
- delete empty redundant knapsack and linear constraints after cleanup in SCIPmatrixCreate()
- cleanup first constraints in SCIPcleanupConssVarbound(), SCIPcleanupConssSetppc(), and SCIPcleanupConssLogicor()
- symmetry handling methods have not been added immediately after computing symmetries, which has been fixed
- delay checking node limits after presolving to correctly continue up to the exceeding main node
- simplified the objective sense assumption for the subproblems in the Lagromory separator
- update effective root depth iteratively to avoid trapping it at a single child node
- fixed that dualsparsify presolver did not always check do-not-multiaggregate variable flag
- fixed bug in computing elements of orbits in orbital reduction
Miscellaneous
-------------
- redefine isrelax to istight in cons_linear.c
Build system
------------
### Cmake
- A file cmake.log containing the changed options is written to the cmake build directory.
- removed replacement of the settings of RelWithDebInfo
- add compile option -ffp-contract=off or /fp:precise to enhance reproducibility across different systems
### Makefile
- add flags -ffp-contract=off and /fp:precise to enhance reproducibility across different systems
Interface changes
-----------------
### New parameters
- added parameter "propagating/symmetry/symtiming" to determine when symmetries are computed and handled
### Changed parameters
- Disabled "propagating/symmetry/addconsstiming" since it is not used anymore.
- Disabled "propagating/symmetry/ofsymcomptiming" since it is not used anymore.
@section RN900 SCIP 9.0.0
*************************
Features
--------
- added simplification of abs(x)^n to x^n when n is even (simplify rule POW12)
- in expression simplification, added possibility to expand power of sum with exponents larger than 2 (simplify rule POW7)
- in expression simplification, added possibility to expand products with sums as factor when there are more than two factors (simplify rule SP12b)
- in expression simplification, added possibility to allow expanding power of products with fractional exponent (simplify rule POW5a)
- can now build with Lapack (used for solving nonlinear problems) explicitly; if IPOPT is used, then Lapack is accessed through it;
an interface to Lapack is available in lapack_calls.h
- added support for logical constraints in binary variables and basic logical operators (and, or, not, equal) to AMPL .nl reader
- indicator constraints now use the same slack variable for the linear constraints if binary variables are used multiple times
for indicator constraints
- new diving heuristic indicatordiving that focuses on indicator variables which control semicontinuous variables
- updated statistics on NLP relaxation; information on convexity of NLP has been added
- added new bandit method (EXP.3-IX) that is the new default of the ALNS heuristic
- added dialog to display recognized permutation symmetries ("display symmetry")
- The symmetry detection code has been completely restructured. Instead of completely encoding symmetry information in
prop_symmetry.c, there is a new callback for constraint handlers, which returns symmetry relevant information by
encoding a constraint as a node and edge colored graph. This way, also custom constraint handlers can provide
symmetry information.
- added special presolving step for logicor and set covering/packing for constraints with two variables and one independent variable
- increased the depth field of the tree structure from 16 to 30 bits and the max depth of the search tree from 65534 to 1073741822
- added new cut selector plugin called cutsel_ensemble. Performs a superset of hybrid cutsel. Implements new filtering methods and scoring options.
- added new branching rule based on Gomory mixed-integer cuts
- added new branching score to the reliability pseudo-cost branching rule
- added new cut selector plugin called cutsel_dynamic. Performs a superset of hybrid cutsel. Implements new filtering methods and scoring options.
- added monoidal strengthening to intersection cut generation of nlhdlr_quadratic
- extended heuristic dps to run after processing the node and to use strict limits for the reoptimization step
- extended obbt propagator to handle variables of the linear constraints corresponding to indicator constraints
- added new heuristic heur_scheduler that models the selection of LNS and diving heuristics as a multi-armed bandit problem
- added nonlinear handler for signomial expressions: adds cuts based on a difference of convex functions representation
- Delayed separators are now called if no other cuts have been found. Previously, such separators were only called near stalling or when the separation rounds limit was reached.
- added a new separator sepa_lagromory to generate Lagromory cuts in a relax-and-cut framework, i.e., GMI cuts generated
at different bases that are explored in the process of solving the Lagrangian dual problem at a node. This separator
is OFF by default.
- when parsing nonlinear constraints from CIP files, the * after the number in a term is now optional if followed by a variable,
i.e., instead of 3*<x>*<y>, now also 3<x>*<y> can be read, but 3<x><y> is not supported;
this allows to read some CIP files that were written with SCIP < 8
- when running bliss, we now limit the number of actually created generators and not the ones considered by bliss
Performance improvements
------------------------
- Variable conflict-based addition of Schreier-Sims cuts for symmetry handling in prop_symmetry.c does no longer use
an expensive explicit conflict graph construction.
- Only run propagation of indicator constraints if relevant variables have changed.
- Propagation of indicator constraints propagates maximal activity of linear constraint to upper bound of slack variable.
- Added initialization of LP relaxation for SOC constraints.
- Avoided some numerical issues when separating SOC constraints.
- If differentation of convex expression fails in convex nlhdlr, then a perturbed point is tried.
- Use sassy/bliss as default symmetry computation package.
- No longer linearize indicator constraints in undercover heuristic by default.
- Deactivate pre-root heuristic zeroobj in undercover heuristic.
- Added new branching score tiebreaker for reliability pseudo-cost branching rule
- Try nearest bound if zero solution value is out of bounds in heuristic trivial.
Interface changes
-----------------
### New and changed callbacks
- Added solution linearization callback for nonlinear handlers.
The nonlinear handler may use this callback to add tight cuts that use the given solution as reference point to the cutpool.
The callback is called if option constraints/nonlinear/linearizeheursol is enabled.
- The callback for copying problem data SCIP_DECL_PROBCOPY() now has a parameter "original" indicating whether the original
or transformed problem should be copied. Similarly, SCIPprobCopy() in prob.h/c has such a parameter.
- Added CONSGETPERMSYMGRAPH and CONSGETSIGNEDPERMSYMGRAPH callback for constraint handlers, which provides symmetry information about constraints to SCIP.
### Deleted and changed API methods
- SCIPtpiInitLock(), SCIPtpiDestroyLock(), SCIPtpiInitCondition(), SCIPtpiDestroyCondition() now take a double
pointer to SCIP_LOCK/SCIP_CONDITION, respectively.
- Renamed SCIPtpiSumbitJob() to SCIPtpiSubmitJob().
- SCIPcreateConsIndicatorLinCons(), SCIPcreateConsIndicatorGenericLinCons() do not allow binvar to be NULL anymore
- Replaced SCIPnlrowSetCurvature() by SCIPsetNlRowCurvature().
- SCIPsnprintf() now returns the required string length in case reallocation is necessary.
- SCIPcomputeCoverUndercover() receives three more arguments which nonlinearities to cover
- removed definition of SQRT
- SCIPincludeObjConshdlr(), SCIPincludeConshdlr(), SCIPconshdlrCreate() receive two more arguments for the
conshdlr callbacks CONSGETPERMSYMGRAPH and CONSGETSIGNEDPERMSYMGRAPH
- removed SYM_VARTYPE, SYM_OPTYPE, SYM_CONSTTYPE, SYM_RHSTYPE, SYM_MATRIXDATA
- new parameter issigned for SCIPcomputeOrbitsSym()
- new parameter symtype for SCIPcomputeComponentsSym()
- new parameter symtype and permvardomaincenter for SCIPlexicographicReductionAddPermutation()
- replaced parameters matrixdata and exprdata of SYMcomputeSymmetryGenerators() by graph
### New API functions
- new functions for interfacing with Lapack: SCIPlapackIsAvailable(), SCIPlapackIsAvailable(), SCIPlapackComputeEigenvalues(), and SCIPlapackSolveLinearEquations
These functions should be used instead of SCIPisIpoptAvailableIpopt(), SCIPcallLapackDsyevIpopt(), and
SCIPsolveLinearEquationsIpopt() in the context of computing eigenvalues or solving linear equations.
If IPOPT is available, the calls will be passed on to Ipopt's interface to Lapack.
- SCIPmultiplyBySumExprSum(), SCIPpowerExprSum()
- SCIPsetParam()
- SCIPgetPrimalDualIntegral() returns the primal dual integral stored in the statistics
- new functions SCIPcreateConsIndicatorLinConsPure() and SCIPcreateConsIndicatorGenericLinConsPure() that
create indicator constraints from a linear constraint without a slack variable
- SCIPgetNLPNlRowsStat() to retrieve counts on linear, convex, and nonconvex rows in NLP
- SCIPnlhdlrSetSollinearize(), SCIPnlhdlrHasSollinearize()
- SCIPbendersGetNLPParam()
- new API functions SCIPlexicographicReductionGetStatistics(), SCIPlexicographicReductionPrintStatistics(),
SCIPlexicographicReductionPropagate(), SCIPlexicographicReductionAddPermutation(), SCIPlexicographicReductionReset(),
SCIPlexicographicReductionFree(), SCIPincludeLexicographicReduction(), for lexicographic reduction.
- new API functions SCIPorbitopalReductionGetStatistics(), SCIPorbitopalReductionPrintStatistics(),
SCIPorbitopalReductionPropagate(), SCIPorbitopalReductionAddOrbitope(), SCIPorbitopalReductionReset(),
SCIPorbitopalReductionFree(), SCIPincludeOrbitopalReduction(), SCIPorbitopalReductionGetDefaultColumnOrdering(),
for orbitopal fixing.
- new API functions SCIPorbitalReductionGetStatistics(), SCIPorbitalReductionPrintStatistics(),
SCIPorbitalReductionPropagate(), SCIPorbitalReductionAddComponent(), SCIPorbitalReductionReset(),
SCIPorbitalReductionFree(), SCIPincludeOrbitalReduction(), for orbital fixing.
- new API functions SCIPgetShadowTreeEventHandlerExecutionTime(), SCIPshadowTreeGetShadowNodeFromNodeNumber(),
SCIPshadowTreeGetShadowNode(), SCIPgetShadowTree(), SCIPactivateShadowTree(), SCIPincludeEventHdlrShadowTree(),
for managing a copy of the branch-and-bound tree for symmetry handling purposes.
- SCIPdotWriteOpening(), SCIPdotWriteNode(), SCIPdotWriteArc(), SCIPdotWriteClosing()
- SCIPincludeCutselEnsemble(), SCIPselectCutsEnsemble() to include cutsel_ensemble or use the selection algorithm
- SCIPincludeBranchruleGomory() includes new gomory cut based branching rule
- SCIPgetVarAvgGMIScore(), SCIPincVarGMISumScore(), SCIPgetVarLastGMIScore(), SCIPsetVarLastGMIScore() set historical values used by SCIP's default branching rule
- SCIPincludeNlhdlrSignomial() includes the signomial nonlinear handler
- SCIPgetExprMonomialData() returns a monomial representation of a product expression
- SCIPestimateRoot() computes estimators for roots with exponent in [0,1]
- SCIPincludeCutselDynamic(), SCIPselectCutsDynamic() to include cutsel_dynamic or use the selection algorithm
- SCIPincludeSepaLagromory() to include the new Lagromory separator
- SCIPconsCompCheck() to compare two constraints based on their check priority
- SCIPgetConsPermsymGraph() and SCIPgetConsSignedPermsymGraph() to access the (signed) permutation symmetry detection graph of a constraint
- SCIPsetConshdlrGetPermsymGraph() and SCIPsetConshdlrGetSignedPermsymGraph() to set the (signed) permutation symmetry detection graph of a constraint
- SCIPconshdlrSupportsPermsymDetection() and SCIPconshdlrSupportsSignedPermsymDetection() to access whether a conshdlr supports detection of (signed) permutation symmetries
- new API functions for creating and manipulating a symmetry detection graph: SCIPcreateSymgraph(), SCIPfreeSymgraph(), SCIPcopySymgraph(), SCIPextendPermsymDetectionGraphLinear(),
SCIPaddSymgraphVarAggregation(), SCIPaddSymgraphOpnode(), SCIPaddSymgraphValnode(), SCIPaddSymgraphConsnode(), SCIPgetSymgraphVarnodeidx(), SCIPgetSymgraphNegatedVarnodeidx(),
SCIPupdateSymgraphLhs(), SCIPupdateSymgraphRhs(), SCIPfixSymgraphVarnode(), SCIPaddSymgraphEdge(), SCIPcomputeSymgraphColors(), SCIPgetSymgraphSymtype(), SCIPgetSymgraphVars(),
SCIPgetSymgraphNVars(), SCIPgetSymgraphNConsnodes(), SCIPgetSymgraphNNodes(), SCIPgetSymgraphNEdges(), SCIPgetSymgraphEdgeFirst(), SCIPgetSymgraphEdgeSecond(),
SCIPgetSymgraphVarnodeColor(), SCIPgetSymgraphNodeType(), SCIPgetSymgraphNodeColor(), SCIPisSymgraphEdgeColored(), SCIPgetSymgraphEdgeColor(), SCIPgetSymgraphNVarcolors(),
SCIPhasGraphUniqueEdgetype(), SCIPallocateSymgraphConsnodeperm(), SCIPcreateSymgraphConsnodeperm(), SCIPgetSymgraphConsnodeperm(), SCIPfreeSymgraphConsnodeperm(),
SCIPgetSymActiveVariables(), SCIPfreeSymDataExpr(), SCIPgetSymExprdataNConstants(), SCIPgetSymExprdataConstants(), SCIPgetCoefSymData(),
SCIPcreateSymOpNodeType(), SCIPgetSymOpNodeType()
- SCIPexprhdlrSetGetSymdata(), SCIPexprhdlrHasGetSymData(), SCIPgetSymDataExpr(), SCIPcallExprGetSymData() to access symmetry data of expressions
- SYMcheckGraphsAreIdentical() to check whether two symmetry detection graphs are identical
- new functions SYMbuildSassyGraph(), SYMbuildSassyGraphCheck()
- new type SYM_GRAPH
- new definitions SCIP_DECL_CONSGETPERMSYMGRAPH, SCIP_DECL_EXPRGETSYMDATA
- new member SYM_NODETYPE_CONS in SYM_NODETYPE enum
- new members SYM_CONSOPTYPE_SUM, SYM_CONSOPTYPE_SLACK, SYM_CONSOPTYPE_COEF, SYM_CONSOPTYPE_RHS, SYM_CONSOPTYPE_LAST in SYM_CONSOPTYPE enum
- new defintion SCIP_DECL_EXPRGETSYMDATA
- new function SCIPdetectSingleOrDoubleLexMatrices()
### Command line interface
- Added optional parameter -i when calling SCIP in AMPL-mode (-AMPL parameter).
If -i is specified, a SCIP shell is started where normally SCIPsolve() would be called.
### Interfaces to external software
- added interface to nauty/traces for symmetry computation
- added interface to sassy, a preprocessor for symmetry computation
- The directory src/sassy contains the source code of sassy.
- Added interface to Lapack (used for solving nonlinear problems).
- The AMPL interface now supports parameters specified in AMPL command scripts via option scip_options.
The value of scip_options is expected to be a sequence of parameter names and values, separated by a space, e.g.,
`option scip_options 'limits/time 10 display/verblevel 1';`.
String values should not be quoted and spaces in string values are not supported.
- sassy can be used now as preprocessor for nauty/traces
- The solution status codes written to AMPL solution files now match those from https://mp.ampl.com/details.html#_CPPv4N2mp3sol6StatusE.
### Changed parameters
- change default value of parameter separating/filtercutpoolrel to FALSE
- Shrunk range of parameter "propagating/symmetry/sstleaderrule" from [0,3] to [0,2], removed "MAXCONFLICTS"-option.
- Removed reading/gmsreader/freeints. A default upper bound of +inf is now assumed for integer variables in GAMS (which is the case since GAMS 23.1).
- Disabled "propagating/symmetry/symfixnonbinaryvars" since it is not used in the new symmetry code.
- Replaced "propagating/symmetry/onlybinarysymmetry" with "propagating/symmetry/enforcecomputesymmetry" and set to FALSE by default.
- Disabled "propagating/symmetry/performpresolving" since running orbital reduction during presolving is not effective.
- Repurposed "propagating/symmetry/usedynamicprop" since it now also applies to lexicographic reduction.
- Changed default value of parameter "propagating/symmetry/addsymresacks" from FALSE to TRUE.
### New parameters
- separating/maxcutsgenfactor and separating/maxcutsrootgenfactor as factors (w.r.t. separating/maxcuts and
separating/maxcutsroot) for limits on the number of cuts generated (which used to be constants '2')
- expr/pow/expandmaxexponent to specify limit on exponent when to expand power of sum
- expr/pow/distribfracexponent to enable expanding power of products with fractional exponents
- expr/product/expandalways to enable expanding any product with sums as factor (that is, also when more than two factors)
- nlhdlr/convex/maxperturb to specify maximal perturbation of non-differential reference points
- benders/default/nlpiterlimit to adjust iteration limit for NLP solver for Benders' decomposition NLP subproblems
- limits/objectivestop to interrupt the solve as soon as a primal solution is found
that is at least as good as the given value
- heuristics/undercover/{coverand,coverind,covernl} to control which nonlinearities to consider (by default only "and" and nonlinear constraints)
- cutselection/ensemble/* all parameters for new ensemble cut selector
- cutselection/dynamic/* all parameters for new dynamic cut selector
- branching/relpscost/gmiavgeffweight specifies the weight in the relpscost branching score of the normalized efficacy of all generated GMI cuts (for a variable)
branching/relpscost/gmilasteffweight specifies the weight in the elpscost branching score of the normalized efficacy of the last generated GMI cut (for a variable)
- nlhdlr/quadratic/usemonoidal to enable monoidal strengthening when separating quadratics with intersection cuts
- nlhdlr/quadratic/trackmore to collect more statistics for monoidal strengthening when separating quadratics with intersection cuts
- nlhdlr/quadratic/useminrep to use the minimal representation to compute cut coefficients when separating quadratics with intersection cuts
- nlhdlr/quadratic/sparsifycuts to enable sparsification of intersection cuts for quadratics
- heuristics/dps/reoptlimits to set strict limits for the reoptimization step in dps
- heuristics/dps/timing to run dps after processing the node
- heuristics/scheduler/* all parameters for new scheduler heuristic
- nlhdlr/signomial/enabled, nlhdlr/signomial/maxnundervars, nlhdlr/signomial/mincutscale: parameters for the signomial nonlinear handler
- separating/lagromory/freq to denote the frequency for calling Lagromory separator
- separating/lagromory/away to denote the minimal integrality violation of a basis variable to try separation
- separating/lagromory/dynamiccuts to denote whether the generated cuts be removed from LP if they are no longer tight
- separating/lagromory/maxroundsroot to denote the maximal number of separation rounds in the root node
- separating/lagromory/maxrounds to denote the maximal number of separation rounds in a non-root node
- separating/lagromory/nmaxcutsperlproot to denote, in the root node, the maximal number of Lagromory cuts that can be
separated per explored basis of the Lagrangian dual
- separating/lagromory/nmaxcutsperlp to denote, in a non-root node, the maximal number of Lagromory cuts that can be
separated per explored basis of the Lagrangian dual
- separating/lagromory/perroundnmaxlpiters to denote the maximal number of separating LP iterations that are allowed per
separation round
- separating/lagromory/dualdegeneracyratethreshold to denote the minimum dual degeneracy rate for the separator execution
- separating/lagromory/varconsratiothreshold to denote the minimum variable-constraint ratio on the optimal face for the
separator execution
- many other advanced parameters for the Lagromory separator, which are also mentioned under separating/lagromory/*
### Data structures
- new data structure SYM_GRAPH to encode symmetry information from a constraint
- new data structure SYM_EXPRDATA to encode symmetry information from expressions
- replaced enum SYM_SYMTYPE by a complete new one; removed SYM_RHSSENSE, added SYM_NODETYPE and SYM_CONSOPTYPE
Deleted files
-------------
- deleted the now unused files: tpi_none.h, tpi_openmp.h, tpi_tnycthrd.h, type_tpi_none.h, type_tpi_openmp.h, type_tpi_tnycthrd.h
Unit tests
----------
- new unittests for nlhdlr_quadratic that test monoidal strengthening and the use of the minimal representation to compute cut coefficients
- unittests for nlhdlr_signomial
Testing
-------
- changed `set lim obj` to `set lim objective` in ctest since `obj` is no longer unambiguous
Build system
------------
### Cmake
- New flag -DLAPACK=on for linking with Lapack (must be available in the system)
- added flag option "SYM=sbliss" for using sassy/bliss as a graph automorphism package
- use SYM=sbliss by default, since sassy and bliss are now shipped with SCIP.
- added flag option "SYM=snauty" for using sassy/nauty as a graph automorphism package
### Makefile
- added flag option "nauty" for SYM variable to specify which graph automorphism package should be used
- added flag option "sbliss" (sassy/bliss) for SYM variable to specify which graph automorphism package should be used
- added flag option "snauty" (sassy/nauty) for SYM variable to specify which graph automorphism package should be used
- use SYM=sbliss by default, since sassy and bliss are now shipped with SCIP
- New flag LAPACK for linking with Lapack (must be available in the system)
- A file scip/config.h is created in the build directory ($(OBJDIR)/include) now.
Defining NO_CONFIG_HEADER is no longer necessary and has no effect anymore.
Fixed bugs
----------
- Number of runs in which separation is enabled will now be correct as per "separating/maxruns" parameter. Earlier,
separation was enabled for "maxruns + 1" number of runs, i.e., separation was enabled even when "maxruns = 0" was set.
- add safeguard for number of selected cuts
- use double double precision for delta in activity updates of cons_linear.c
- sort constraints in checkSolOrig() to keep the logic of constraint handlers intact
- fixed make install when SHARED=no and make uninstall
- check absolute coefficients relative to extremal average to avoid invalid unifications in normalizeCons()
- enforce and check symmetry-based constraints to take their locks (in dual reductions) into account
- flush changes at the end of SCIPlpiSetBase() in lpi_grb.c to apply the newly set basis correctly
Miscellaneous
-------------
- The TPI has been changed to become mostly independent from the actual parallel interface during compile time.
For this, the locks and conditions are now pointers to abstract structs.
- fixed that scip/def.h, the header for C preprocessor definition (`#define`'s), included headers for some SCIP type and function definitions
(scip/type_retcode.h, scip/type_message.h, scip/pub_message.h)
@page RN8 Release notes for SCIP 8
@section RN810 SCIP 8.1.0
*************************
Fixed bugs
----------
- fixed that scaling of rows in Gurobi interface (SCIPlpiScaleRow()) changed infinite sides to large finite ones (1e20) when scale factor is negative
- check whether objective limit is truly reached in SCIPlpiIsStable()
- if an objective limit is set and Mosek claims that it is exceeded, check that this is indeed the case in SCIPlpiIsStable()
- the .mps file reader was extended to additionally accept .mps files with the objective sense section on one line
- ensure that delayed cutpool separation does not happen if enough cuts have been found already
- fixed that a Gurobi or Mosek interface (LPI) could not be freed from a thread different than the one it was created in, which lead to problems when, e.g., using the concurrent optimizer
- in cons_varbound if both variables are fixed, instead of propagating the constraint check the feasibility of the constraint since propagating can lead to unnecessary numerical troubles
- fixed memory leak in branching rule "distribution"
- fixed that undercover did not enforce that sufficiently many variables in an and-constraints were fixed to have it linearized in the generated sub-scip
- fixed two bugs in cons_varbound: avoid adding variable bounds if vbdcoef is infinite and unlock/lock variables if lhs/rhs/vbdcoef are changed
- globalize constraint changes before bound changes during the effective root shift in treeSwitchPath() to correctly update variable locks by avoiding global bounds with outstanding bound change events when deleting constraints
- fixed error when attempting to copy SCIP with activated pricers
- remove integrality check for implicit integral variables in cons_integral.c, updated the definition for variable type implicit integer to be more explicit that these variables can take fractional values, and updated FAQ entry
- updated and, or, and pseudoboolean constraint handlers to better handle fractional implicit integer variables in enforcement
- avoid invalid strong Chvatal-Gomory cuts by ceiling with tolerance in the calculation of parameter k and flooring slack coefficients with standard epsilon tolerance as well as quad precision
- add missing row links to columns in SCIPflushRowExtensions() required to maintain correct row norms
- restrict separator intobj to solutions for which there can be no better feasible integral objective values to avoid cutting them off
- delay removal of clique lists from SCIPvarRemoveCliquesImplicsVbs() into cliqueCleanup() to avoid segmentation faults by incomplete cleanups after variable conversions
- reject sub-solutions with invalid objectives in SCIPtranslateSubSols() due to contradicting infinite contributions
- correct column index in getMinMaxActivityResiduals() to make presolver dualinfer work
- copy quiet flag from main scip's message handler to the one of solverscip in concurrent optimization
- avoid bound tightening cycles towards huge redundancy bounds in fullDualPresolve() to avert fatal numerical trouble in representing vertices of linear relaxations with unbounded domains
- fix problem where debug solution did not work if branching constraints are present
- update index of dominating variable on coefficient deletion in dualPresolving() of constraint handler logicor
- pass on flags from a redundant to the implying varbound constraint in preprocessConstraintPairs() to avoid suboptimal fixings by model relaxations
- apply reductions of dualinfer only if a dual solution exists (primal is bounded)
- before presolving is finished check solutions before retransforming them including tiny values to keep check flags consistent
- disable heuristics before and during presolving in benders decomposition to avoid messing up the objective structure in the solution store by dropping auxiliary variables in the required retransformations
- correct local flag of singleton conflict constraints in tightenSingleVar() against invalid bound globalization
- respect unboundedness in the computation of activity bounds in conflict.c to avoid invalid huge bounds due to small coefficients on unbounded variables
- ensure positive sides of a linear constraint when recognizing a set partition in rangedRowSimplify() to account for redundancy issues
- relax numerical conditions for variable aggregations to avert invalid variable fixings
- fixed harmless read of uninitialized data when creating parameters
- fix call of SCIPnlpiOraclePrintProblem in nlpi_worhp
Performance improvements
------------------------
- Use sassy/bliss as default symmetry computation package.
Interface changes
-----------------
### Interfaces to external software
- added interface to nauty/traces for symmetry computation
- added interface to sassy, a preprocessor for symmetry computation
- The directory src/sassy contains the source code of sassy.
Build system
------------
### Cmake
- added flag option "SYM=sbliss" for using sassy/bliss as a graph automorphism package
### Makefile
- added flag option "nauty" for SYM variable to specify which graph automorphism package should be used
- added flag option "sbliss" for SYM variable to specify which graph automorphism package should be used
- use SYM=sbliss by default, since sassy and bliss are now shipped with SCIP
Miscellaneous
-------------
- the parameter change callback is no longer called at the moment a parameter is created
@section RN804 SCIP 8.0.4
*************************
Features
--------
- use quad precision in cutsSubstituteMIR() for substituting slack variables into CMIR cuts
- use quad precision for activity computations in cons_linear.c
### Deleted and changed API methods
- SCIPshrinkDisjunctiveVarSet() no longer attempts to cutoff the current node if it finds the
given disjunction to be infeasible; it is now in the responsibility of the caller to act accordingly
### New API functions
- added SCIPskipSpace
- added XML parser routines from src/xml/xml.h
### Interfaces to external software
- updated XPRESS interface to work with XPRESS 41 as well
- new interface to LP solver HiGHS (lpi_highs.cpp)
### Changed parameters
- changed integer parameter "propagating/symmetry/recomputrestart" from range {0, 1, 2} to being fixed at value 0
Unit tests
----------
- added new checks for objective, bounds and sides inside the scaling tests in lpi/change.c
Fixed bugs
----------
- relax condition of assert in lpSolve to hold only if lp/checkstability is true
- OPB reader: dynamically increase the size of the line buffer for reading in getMaxAndConsDim()
- Enabled the solution limit checks in SCIPsolveIsStopped in solve.c when in SCIP_STAGE_PRESOLVING
- fix quad precision comparison for the calculation of knapsackcover constraints.
- force copying of symmetry constraints for concurrent solve
- increase the precision of double multiplications in quad precision environments
- corrected handling of different variable types in symmetry
- orbitope detection: refine computation of overlap structure and fixed bug in finding orbitope generators
- ensure that winner is always determined in concurrent mode
- when a row with invalid index range is added to the global cutpool, update the indices instead of failing with an assert
- update of watched literals in cons_xor.c and ensure that fixed variables are counted in propacateCons()
- avoid some numerical issue in check for redundant variables in linear constraints (introduced with version 8.0.2)
- more rows are treated as being integral in cutsSubstituteMIR() for CMIR cuts
- fixed several relaxations of the rhs of cuts to 0 in cuts.c
- avoid aggregation into a single linear constraint if they should not be upgraded (needed for indicator constraints)
- apply effective root changes before fork is repropagated during treeSwitchPath() in tree.c
- avoid invalid objective value for solutions generated from an unbounded LP relaxation in case of a nonlinear objective function
- disable recomputing symmetries after a restart (constraint removal is not permitted)
- avoid cutting off optimal solutions for small feasibility tolerances in conflict analysis
- initialize variable in presol_dualsparsify.c
- fix in presolving of variable bound constraints to use absolute instead of relative difference
- free variable histories in reoptimization mode
- handle whitespaces in interactive shell history consistently
- check and enforce equalities on which the objective is projected in cons_linear.c
- ensure row feasibilities of solution shiftings in heur_oneopt.c and heur_twoopt.c
- remove rounded row check blocking tolerable primal solutions in cons_varbound.c
- fixed that presolve of logicor-constraints may have attempted to cutoff a root of the not yet existing branch-and-bound tree
- only consider positive slack variables as active in benders.c
- in the feasibility check of and/or constraints, allow for fractional values in operands
- fixed linear outer-approximation for some composite absolute-value expressions
Miscellaneous
-------------
- Extended documentation of the parameter limits/solutions to point out that the limit is first checked in presolving
- Added more information about using SCIPcache- and SCIPflushRowExtensions() to documentation and comments
- Extended the `how to add' sections of the documentation by adding information on how to include default plugins into SCIP
@section RN803 SCIP 8.0.3
*************************
Examples and applications
-------------------------
- Externalize STP and PolySCIP applications
Interface changes
-----------------