Merge remote-tracking branch 'origin/v80-bugfix'

CHANGELOG

@@ -219,6 +219,7 @@ Fixed bugs
 - 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
 
 @section RN804 SCIP 8.0.4
 *************************

check/CMakeLists.txt

@@ -476,6 +476,7 @@ set(pairs_Issue
     "instances/Issue/3625.lp\;117.75284354701\;default"
     # Test currently not working since problems with the feasibility check for unbounded problems appear: https://git.zib.de/integer/scip/-/issues/3422
     # "instances/Issue/3629.cip\;-infinity\;only_dualinfer"
+    "instances/Issue/3632.cip\;0\;default"
 )
 
 #

check/instances/Issue/3632.cip

@@ -0,0 +1,15 @@
+STATISTICS
+  Problem name     : mod011
+  Variables        : 4 (3 binary, 0 integer, 0 implicit integer, 1 continuous)
+  Constraints      : 0 initial, 2 maximal
+OBJECTIVE
+  Sense            : minimize
+VARIABLES
+  [binary] <x1>: obj=1, original bounds=[0,1]
+  [binary] <x2>: obj=1, original bounds=[0,1]
+  [binary] <x3>: obj=1, original bounds=[0,1]
+  [continuous] <x10269>: obj=0, original bounds=[0,+inf]
+CONSTRAINTS
+  [linear] <c154>: <x10269>[C] == 94;
+  [linear] <c2>: 0 <= <x1>[B] +<x2>[B] +<x3>[B] <= 1;
+END

src/scip/cons_linear.c

@@ -11424,11 +11424,10 @@ SCIP_DECL_SORTINDCOMP(consdataCompSim)
    return (value > 0 ? +1 : (value < 0 ? -1 : 0));
 }
 
-/** tries to simplify coefficients and delete variables in ranged row of the form lhs <= a^Tx <= rhs, e.g. using the greatest
- *  common divisor
+/** tries to simplify coefficients in ranged row of the form lhs <= a^Tx <= rhs
  *
- *  1. lhs <= a^Tx <= rhs, forall a_i >= lhs, a_i <= rhs, and forall pairs a_i + a_j > rhs then we can change this
- *     constraint to 1^Tx = 1
+ *  1. lhs <= a^Tx <= rhs, x binary, lhs > 0, forall a_i >= lhs, a_i <= rhs, and forall pairs a_i + a_j > rhs,
+ *     then we can change this constraint to 1^Tx = 1
  */
 static
 SCIP_RETCODE rangedRowSimplify(
@@ -11465,16 +11464,21 @@ SCIP_RETCODE rangedRowSimplify(
    if( nvars < 2 )
       return SCIP_OKAY;
 
+   lhs = consdata->lhs;
+   rhs = consdata->rhs;
+   assert(!SCIPisInfinity(scip, -lhs));
+   assert(!SCIPisInfinity(scip, rhs));
+   assert(!SCIPisNegative(scip, rhs));
+
+   /* sides must be positive to detect set partition */
+   if( !SCIPisPositive(scip, lhs) || !SCIPisPositive(scip, rhs) )
+      return SCIP_OKAY;
+
    vals = consdata->vals;
    vars = consdata->vars;
    assert(vars != NULL);
    assert(vals != NULL);
 
-   lhs = consdata->lhs;
-   rhs = consdata->rhs;
-   assert(!SCIPisInfinity(scip, -lhs) && !SCIPisInfinity(scip, rhs));
-   assert(!SCIPisNegative(scip, rhs));
-
    minval = SCIP_INVALID;
    secondminval = SCIP_INVALID;
    maxval = -SCIP_INVALID;
@@ -11504,7 +11508,7 @@ SCIP_RETCODE rangedRowSimplify(
       if( SCIPisEQ(scip, minval, maxval) && SCIPisEQ(scip, lhs, rhs) )
          return SCIP_OKAY;
 
-      /* check if we can and need to choose exactly one binary variable */
+      /* check if we can choose one and need to choose at most one binary variable */
       if( SCIPisGE(scip, minval, lhs) && SCIPisLE(scip, maxval, rhs) && SCIPisGT(scip, minval + secondminval, rhs) )
       {
          /* change all coefficients to 1.0 */