SCIP 1.0.0

Features

the doxygen documentation now has HowTo's for all plugin types
the doxygen documentation now contains a FAQ
SCIP now has a couple of specialized settings, all called scip_*.set
SCIP is now compatible to the Exception branch of SoPlex
presolving, cut separation, primal heuristics and strong branching now better respect time limit
time limit is now forwarded to lp solving algorithm
modified cut selection code
cut conversion into linear constraints after a restart now works better
if possible, objective function is scaled to make objective value integral with gcd 1
removed performance bottleneck with non-bfs based node selectors and large leaf queues at the cost of a small memory overhead (2 ints per node in the leaf queue); this improves performance quite a bit on instances that take a large number of branching nodes
slightly modified automatic constraint aging strategy
the documentation has now a TAB Modules; there you can find list of available constraint handles, presolvers, propagators, lpi interfaces, file readers and so on
Plugins
- new C templates disp_xxx.h and dialog_xxx.h and C++ wrapper classes objdisp.h and objdialog.h, respectively
- new improvement heuristic "oneopt"
- improved performance of linear constraint propagation by delaying some floor/ceil calculations
- new node selection rule "estimate" (best estimate search)
- best estimate search is now used in all large neighborhood search heuristics
- new heuristic "actconsdiving" following an idea of John Chinneck
- new node selection rule "hybridestim"
- improved performance of clique cut separator
- modified reader "sol", st. files which where created via typing the order of commands 'set log *.sol', 'disp sol var -', 'set log cplex.log' in Cplex can now be read
- modified probing presolver to do multiple cycles if called in subsequent runs
- greatly improved performance of LP file reader by replacing string copies with pointer copies
- changed sort algorithm in probing presolver
- added flow cover separator
- gomory cuts are now also separated for integral slack variables
- less aggressive in Gomory cut separation
- strong CG cuts are now also separated for integral slack variables
- new dummy LP interface "lpi_none.c"; useful for running SCIP without a LP solver

Interface changes

New and changed callbacks

new callback method SCIPdialogFree()

Deleted and changed API methods

slightly modified bound substitution heuristic in SCIPcalcMIR() and SCIPcalcStrongCG()
slightly less conservative in numerics for SCIPmakeRowIntegral()
linear and knapsack constraint handler may now deal with coefficients of value zero
calling SCIPwriteLP is now possible in Solved Stage
new parameter "maxbounddist" for SCIPincludeSepa() and constructor ObjSepa()
removed parameter "branchdir" from SCIPbranchVar()
new parameters "leftchild", "eqchild" and "downchild" for SCIPbranchVar()
new parameter "estimate" for SCIPcreateChild()
removed method SCIPnodeGetPriority()
new parameter "restart" for method SCIPfreeSolve()
SCIPgetVarStrongbranch() now also returns lperror == TRUE if the solving process should be stopped, e.g., because of a time limit
removed parameter "lowestboundfirst" from SCIPincludeNodesel()
replaced methods SCIPvarGetClosestVlb() and SCIPvarGetClosestVub() from pub_var.h by new methods SCIPgetVarClosestVlb() and SCIPgetVarClosestVlb() in scip.h
modified SCIP_SUBVERSION to be a number instead of a string (to be able to use #if SCIP_SUBVERSION >gt;= ...)
SCIPsubversion() now returns an int instead of a const char*
new parameter "force" for SCIPtightenVarLb() and SCIPtightenVarUb()

New API functions

SCIPreadSol()
SCIPgetVarRedcost()
SCIPnodeUpdateLowerboundLP()
SCIPwriteMIP()
SCIPsepaGetMaxbounddist()
SCIPcalcNodeselPriority()
SCIPnodeGetEstimate()
SCIPgetLocalOrigEstimate() and SCIPgetLocalTransEstimate()
SCIPnodeGetDomchg()
SCIPboundchgGetNewbound(), SCIPboundchgGetVar(), SCIPboundchgGetBoundchgtype(), SCIPboundchgGetBoundtype(), SCIPboundchgIsRedundant(), SCIPdomchgGetNBoundchgs(), SCIPdomchgGetBoundchg()
SCIPisStopped()
SCIProwIsInGlobalCutpool()
SCIPresetParams()
SCIPtightenVarLbGlobal() and SCIPtightenVarUbGlobal()
SCIPgetRootNode() (in combination with SCIPcutoffNode(), this allows the immediate finishing of the optimization)

Command line interface

default dialog menu now includes the commands "set default" and "display parameters"
added option to write node LP and MIP relaxations to LP file from interactive shell

Changed parameters

parameters are now separated into basic and advanced, the latter ones have been moved to extra submenus
priority parameters are now restricted to be in [INT_MIN/4,INT_MAX/4] to avoid overflow errors in comparison methods
increased priority of "estimate" node selector, such that this is the new default node selector
changed default value of global "separating/maxbounddist" to 1.0
changed default value of "numerics/boundstreps" to 0.05 in order to avoid very long propagation loops on continuous variables
changed default value of "separating/objparalfac" to 0.01 for performance reasons
changed default values of "heuristics/∗diving/backtrack to TRUE
changed default value of "nodeselection/restartdfs/stdpriority" to 10000
changed meaning of parameter setting "nodeselection/childsel = l"; old meaning is now called 'r'
changed default value of "presolving/restartfac" to 0.05
changed default value of "presolving/restartminred" to 0.10
changed default value of "constraints/linear/propfreq" to 1
changed default value of "separating/objparalfac" to 0.0001
changed default value of "conflict/maxvarsfac" to 0.1
changed default value of "conflict/useprop" to TRUE
changed default value of "conflict/useinflp" to TRUE
changed default value of "conflict/usepseudo" to TRUE
changed default value of "conflict/maxlploops" to 2
changed default value of "conflict/lpiterations" to 10
changed default value of "conflict/interconss" to -1
changed default value of "conflict/reconvlevels" to -1
changed default value of "conflict/settlelocal" to FALSE

New parameters

"conflict/enable" to globally enable or disable conflict analysis
"constraints/linear/maxcardbounddist" and "constraints/knapsack/maxcardbounddist"
"heuristics/∗diving/backtrack" to activate 1-level backtracking for most of the diving heuristics
"heuristics/feaspump/maxstallloops"
"nodeselection/childsel" to control the child selection
"presolving/immrestartfac"
"separating/∗/maxbounddist" to have individual maxbounddist parameters per separator
"separating/clique/backtrackfreq" to speed up clique cut separation in heuristic fashion
"separating/redcost/continuous"

Build system

Makefile

added .exe extension to binaries of MinGW
added "LPS=none" for compiling SCIP without a LP solver
modified the default LP solver to be SoPlex instead of CPLEX
removed the ".static" extension associated to the LINK variable from the Makefile system (If you want to build makefiles for shared library generation, use the OPT variable. For example, you could create a makefile "make/make.linux.x86.gnu.opt-shared" and compile it with "make OPT=opt-shared".)
added version numbers to library files (There will be a softlink generated in the lib/ and bin/ directories without version number that point to the latest compiled version.)
made ZIMPL=true the default; if you do not want to include ZIMPL support, call "make ZIMPL=false"

Fixed bugs

fixed bug in rowScale() concerning deletion of almost zero coefficients
fixed bug in SCIPcutpoolAddNewRow() concerning update of minidx and maxidx of added row
removed wrong assert in bounddisjunction constraint enforcement
fixed bug with wrong bound changes of loose variables
fixed bug with aggregated variables in debug solution test
fixed numerical buf with slightly different LP optimum after resolving due to probing/diving
fixed bug in cmir and flowcover separator with variables which are currently not in the LP
weakened assert in primal.c in order to avoid numerical troubles
changed wrong assert in SCIPnodeAddBoundinfer()
fixed bug in intshifting and oneopt heuristic with variables which are currently not in the LP
fixed bug in integer objective seperator with restarts
fixed bug in integer objective seperator with dynamic columns
fixed numerical bug in propagator of varbound constraint handler
fixed numerical bug in rowScaling of lp.c, which possibly cut off feasible solutions
fixed bug with too long variable names
fixed bug with strange user descriptions of plugins
changed position of some asserts to prevent segmentation faults
SCIPgetAvgPseudocostCount() and SCIPgetAvgPseudocostCountCurrentRun() now return the average over all integer variables instead of all variables, since pseudo costs are not recorded for continuous variables
fixed wrong sorting of plugins with priorities close to INT_MIN or INT_MAX
replaced "line" by "read" in Makefile, since "line" is non-standard
fixed bug in variable bound constraint handler with changing bounds on multi-aggregated variables
fixed bug in variable bounds search and insertion method
fixed bug with LP size management in probing if column generation is used
fixed bug with branching rules that produce only one child with no changes to the problem
fixed bug in linear constraint handler: only tight cuts are transformed into linear constraints after restart
fixed bug in LP file reader with row names identical to section keywords
fixed bug that external relaxator is not reset appropriately for a new problem instance
fixed potential bugs due to errors in resolving the LP after diving or probing
removed wrong assert in function paramWrite()
fixed potential bugs in SCIPpriceLoop() and priceAndCutLoop(), st. now all LP solution stati are handled appropriately
fixed bug with uninitialized in check.awk
fixed bug with primal heuristics reducing the cutoff bound such that the current node is cut off
now it is possible to add original solutions
fixed bug that cut age was not reset to zero for violated cuts
fixed bugs with SCIPgetBestsol() returning NULL after a restart with user objective limit
fixed wrong status code in presence of user objective limit and a feasible solution that is not better than the limit
fixed bug regarding modifying bounds in original problem if negated original variables exist
fixed bug in ZIMPL file reader for multiple occurrences of a single variable in the objective function
fixed bug with deleting variables from the transformed problem that are contained in the implication graph
fixed bug in oneopt heuristic: must not be called on pseudo nodes if continuous variables are present
significantly improved performance of c-MIR and Gomory cuts by caching closest VLB and VUB info
fixed bug in root reduced cost fixing propagator that leads to an empty domain for a variable as a proof of optimality of the current incumbent
fixed bug in bounddisjunction constraint handler with propagation of multi-aggregated variables
fixed bug with almost integral multi-aggregation in dual presolve of linear constraint handler
fixed bug with numerics in update of min/maxactivity in linear constraint handler
fixed bug with numerics in linear constraint handler due to non-representable BOUNDSCALETOL
SCIPwrite{LP,MIP} may no longer be called after solving, since the LP data structures may not be valid
fixed potential bug with non-existent LP in SCIPwrite{LP,MIP}
fixed bug with multiple pending bound changes on some variable
fixed bug with fractional coefficients of binary variables in cont –>gt; impl int upgrading