Merge branch 'strongbranching_dynamiclookahead_lognormal' into 'master'

Dynamic Lookahead SB

See merge request integer/scip!3618

Author: GioniMexi

CHANGELOG

@@ -32,6 +32,8 @@ Features
   the problem is now solved in a Benders' decomposition relaxator; instead of decomposing the original SCIP instance, the relaxator builds the decomposed problem in
   sub-SCIPs and solves it via default Benders' Decomposition; a solution to the original (undecomposed) problem is now made available by the relaxator;
   the SCIP shell dialog "display statistics" now also prints the statistics from solving the Benders' decomposition in the relaxator
+- added a dynamic max-lookahead criterion for strong branching. Fits a probability distribution to the observed candidate gains and
+  stop evaluating further candidates once the expected tree-size reduction no longer justifies the LP evaluation cost.
 
 Performance improvements
 ------------------------
@@ -193,6 +195,9 @@ Interface changes
   solving after the completion of the Benders' decomposition algorithm if the problem is not solved to optimality. The
   "nodelimit" parameter allows the user to provide a node limit for the Benders' decomposition master problem (by
   default the limits from the original SCIP instance are copied to the master problem).
+- new parameters "branching/relpscost/dynamiclookahead", "branching/relpscost/dynamiclookaheadquot", "branching/relpscost/dynamiclookdistribution",
+  and "branching/relpscost/minsamplesize" to configure the dynamic max-lookahead criterion for strong branching: enable flag, fraction threshold,
+  distribution choice, and minimum sample size.
 
 ### Data structures
 

src/scip/branch.c

@@ -466,7 +466,7 @@ SCIP_RETCODE SCIPbranchcandGetExternCands(
    int*                  nprioexterncands,   /**< pointer to store the number of candidates with maximal priority, or NULL */
    int*                  nprioexternbins,    /**< pointer to store the number of binary candidates with maximal priority, or NULL */
    int*                  nprioexternints,    /**< pointer to store the number of integer candidates with maximal priority, or NULL */
-   int*                  nprioexternimpls    /**< pointer to store the number of implicit integer candidates with maximal priority, 
+   int*                  nprioexternimpls    /**< pointer to store the number of implicit integer candidates with maximal priority,
                                               *   or NULL */
    )
 {
@@ -643,7 +643,7 @@ SCIP_RETCODE SCIPbranchcandAddExternCand(
    {
       /* candidate has equal priority as the current maximum:
        * move away the first non-maximal priority candidate, move the current candidate to the correct
-       * slot (binaries first, integers next, implicit integers next, continuous last) and increase the number 
+       * slot (binaries first, integers next, implicit integers next, continuous last) and increase the number
        * of maximal priority candidates
        */
       if( insertpos != branchcand->nprioexterncands )
@@ -675,11 +675,11 @@ SCIP_RETCODE SCIPbranchcandAddExternCand(
             assert(vartype != SCIP_VARTYPE_CONTINUOUS);
             if( insertpos != branchcand->nprioexternbins + branchcand->nprioexternints )
             {
-               branchcand->externcands[insertpos] = 
+               branchcand->externcands[insertpos] =
                   branchcand->externcands[branchcand->nprioexternbins + branchcand->nprioexternints];
-               branchcand->externcandsscore[insertpos] = 
+               branchcand->externcandsscore[insertpos] =
                   branchcand->externcandsscore[branchcand->nprioexternbins + branchcand->nprioexternints];
-               branchcand->externcandssol[insertpos] = 
+               branchcand->externcandssol[insertpos] =
                   branchcand->externcandssol[branchcand->nprioexternbins + branchcand->nprioexternints];
 
                insertpos = branchcand->nprioexternbins + branchcand->nprioexternints;
@@ -793,7 +793,7 @@ SCIP_Bool SCIPbranchcandContainsExternCand(
       }
       /* the variable is continuous, look at the slots containing continuous variables */
       assert(vartype == SCIP_VARTYPE_CONTINUOUS);
-      for( i = branchcand->nprioexternbins + branchcand->nprioexternints + branchcand->nprioexternimpls; 
+      for( i = branchcand->nprioexternbins + branchcand->nprioexternints + branchcand->nprioexternimpls;
            i < branchcand->nprioexterncands; i++ )
          if( branchcand->externcands[i] == var )
             return TRUE;
@@ -2326,7 +2326,7 @@ SCIP_Real SCIPbranchGetScoreMultiple(
 /** computes a branching point for a (not necessarily discrete) variable
  * a suggested branching point is first projected onto the box
  * if no point is suggested, then the value in the current LP or pseudo solution is used
- * if this value is at infinity, then 0.0 projected onto the bounds and then moved inside the interval is used 
+ * if this value is at infinity, then 0.0 projected onto the bounds and then moved inside the interval is used
  * for a discrete variable, it is ensured that the returned value is fractional
  * for a continuous variable, the parameter branching/clamp defines how far a branching point need to be from the bounds of a variable
  * the latter is only applied if no point has been suggested, or the suggested point is not inside the variable's interval
@@ -2385,7 +2385,7 @@ SCIP_Real SCIPbranchGetBranchingPoint(
       else if( (SCIPsetIsInfinity(set, -lb) || SCIPsetIsRelGT(set, branchpoint, lb)) &&
                 (SCIPsetIsInfinity(set,  ub) || SCIPsetIsRelLT(set, branchpoint, ub)) )
       {
-         /* if it is continuous and inside the box, then accept it */ 
+         /* if it is continuous and inside the box, then accept it */
          return branchpoint;
       }
       /* if it is continuous and suggestion is one of the bounds, continue below */
@@ -2445,7 +2445,7 @@ SCIP_Real SCIPbranchGetBranchingPoint(
          branchpoint = 0.0;
    }
    else if( SCIPsetIsInfinity(set, -branchpoint) )
-   { 
+   {
       /* if value is at -infty, then the lower bound should be at -infinity */
       assert(SCIPsetIsInfinity(set, -lb));