Support for AND-constraints (#980)

* Support for AND-constraints

* better spacing in pxd

* some debugging

* Add two missing methods. Will not test

* fix memory leak

Author: Joao-Dionisio

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 ### Added
+- More support for AND-Constraints
 - Added support for knapsack constraints
 - Added isPositive(), isNegative(), isFeasLE(), isFeasLT(), isFeasGE(), isFeasGT(), isHugeValue(), and tests
 - Added SCIP_LOCKTYPE, addVarLocksType(), getNLocksDown(), getNLocksUp(), getNLocksDownType(), getNLocksUpType(), and tests

src/pyscipopt/scip.pxd

@@ -1653,6 +1653,13 @@ cdef extern from "scip/cons_and.h":
                                          SCIP_Bool dynamic,
                                          SCIP_Bool removable,
                                          SCIP_Bool stickingatnode)
+    int          SCIPgetNVarsAnd(SCIP* scip, SCIP_CONS* cons)
+    SCIP_VAR**   SCIPgetVarsAnd(SCIP* scip, SCIP_CONS* cons)
+    SCIP_VAR*    SCIPgetResultantAnd(SCIP* scip, SCIP_CONS* cons)
+    SCIP_Bool    SCIPisAndConsSorted(SCIP* scip, SCIP_CONS* cons)
+    SCIP_RETCODE SCIPsortAndCons(SCIP* scip, SCIP_CONS* cons)
+    SCIP_RETCODE SCIPchgAndConsCheckFlagWhenUpgr(SCIP* scip, SCIP_CONS* cons, SCIP_Bool flag)
+    SCIP_RETCODE SCIPchgAndConsRemovableFlagWhenUpgr(SCIP* scip, SCIP_CONS* cons, SCIP_Bool flag)
 
 cdef extern from "scip/cons_or.h":
     SCIP_RETCODE SCIPcreateConsOr(SCIP* scip,

src/pyscipopt/scip.pxi

@@ -5990,6 +5990,160 @@ cdef class Model:
 
         return vars
 
+    def getNVarsAnd(self, Constraint and_cons):
+        """
+        Gets number of variables in and constraint.
+
+        Parameters
+        ----------
+        and_cons : Constraint
+            AND constraint to get the number of variables from.
+
+        Returns
+        -------
+        int
+
+        """
+        cdef int nvars
+        cdef SCIP_Bool success
+
+        return SCIPgetNVarsAnd(self._scip, and_cons.scip_cons)
+
+    def getVarsAnd(self, Constraint and_cons):
+        """
+        Gets variables in AND constraint.
+
+        Parameters
+        ----------
+        and_cons : Constraint
+            AND Constraint to get the variables from.
+
+        Returns
+        -------
+        list of Variable
+
+        """
+        cdef SCIP_VAR** _vars
+        cdef int nvars
+        cdef SCIP_Bool success
+        cdef int i
+
+        constype = bytes(SCIPconshdlrGetName(SCIPconsGetHdlr(and_cons.scip_cons))).decode('UTF-8')
+        assert(constype == 'and', "The constraint handler %s does not have this functionality." % constype)
+
+        nvars = SCIPgetNVarsAnd(self._scip, and_cons.scip_cons)
+        _vars = SCIPgetVarsAnd(self._scip, and_cons.scip_cons)
+
+        vars = []
+        for i in range(nvars):
+            ptr = <size_t>(_vars[i])
+            # check whether the corresponding variable exists already
+            if ptr in self._modelvars:
+                vars.append(self._modelvars[ptr])
+            else:
+                # create a new variable
+                var = Variable.create(_vars[i])
+                assert var.ptr() == ptr
+                self._modelvars[ptr] = var
+                vars.append(var)
+
+        return vars
+
+    def getResultantAnd(self, Constraint and_cons):
+        """
+        Gets the resultant variable in And constraint.
+
+        Parameters
+        ----------
+        and_cons : Constraint
+            Constraint to get the resultant variable from.
+
+        Returns
+        -------
+        Variable
+
+        """
+        cdef SCIP_VAR* _resultant
+        cdef SCIP_Bool success
+
+        _resultant = SCIPgetResultantAnd(self._scip, and_cons.scip_cons)
+
+        ptr = <size_t>(_resultant)
+        # check whether the corresponding variable exists already
+        if ptr not in self._modelvars:
+            # create a new variable
+            resultant = Variable.create(_resultant)
+            assert resultant.ptr() == ptr
+            self._modelvars[ptr] = resultant
+        else:
+            resultant = self._modelvars[ptr]
+            
+        return resultant
+
+    def isAndConsSorted(self, Constraint and_cons):
+        """
+        Returns if the variables of the AND-constraint are sorted with respect to their indices.
+
+        Parameters
+        ----------
+        and_cons : Constraint
+            Constraint to check.
+
+        Returns
+        -------
+        bool
+
+        """
+        cdef SCIP_Bool success
+
+        return SCIPisAndConsSorted(self._scip, and_cons.scip_cons)
+
+    def sortAndCons(self, Constraint and_cons):
+        """
+        Sorts the variables of the AND-constraint with respect to their indices.
+
+        Parameters
+        ----------
+        and_cons : Constraint
+            Constraint to sort.
+
+        """
+        cdef SCIP_Bool success
+
+        PY_SCIP_CALL(SCIPsortAndCons(self._scip, and_cons.scip_cons))
+    
+    def chgAndConsCheckFlagWhenUpgr(self, Constraint cons, flag):
+        """
+        when 'upgrading' the given AND-constraint, should the check flag for the upgraded 
+        constraint be set to TRUE, even if the check flag of this AND-constraint is set to FALSE?
+        
+        Parameters
+        ----------
+        cons : Constraint
+            The AND constraint to change.
+        flag : bool
+            The new value for the check flag.
+
+        """
+
+        PY_SCIP_CALL(SCIPchgAndConsCheckFlagWhenUpgr(self._scip, cons.scip_cons, flag))
+
+    def chgAndConsRemovableFlagWhenUpgr(self, Constraint cons, flag):
+        """
+        when 'upgrading' the given AND-constraint, should the removable flag for the upgraded 
+        constraint be set to TRUE, even if the removable flag of this AND-constraint is set to FALSE?
+        
+        Parameters
+        ----------
+        cons : Constraint
+            The AND constraint to change.
+        flag : bool
+            The new value for the removable flag.
+
+        """
+
+        PY_SCIP_CALL(SCIPchgAndConsRemovableFlagWhenUpgr(self._scip, cons.scip_cons, flag))
+
     def printCons(self, Constraint constraint):
         """
         Print the constraint

tests/test_cons.py

@@ -72,6 +72,23 @@ def test_cons_logical():
     assert m.isEQ(m.getVal(result1), 1)
     assert m.isEQ(m.getVal(result2), 0)
 
+def test_cons_and():
+    m = Model()
+    x1 = m.addVar(vtype="B")
+    x2 = m.addVar(vtype="B")
+    result = m.addVar(vtype="B")
+
+    and_cons = m.addConsAnd([x1, x2], result)
+
+    assert m.getNVarsAnd(and_cons) == 2
+    assert m.getVarsAnd(and_cons) == [x1, x2]
+    resultant_var = m.getResultantAnd(and_cons)
+    assert resultant_var is result
+    m.optimize()
+
+    m.sortAndCons(and_cons)
+    assert m.isAndConsSorted(and_cons)
+    
 def test_cons_logical_fail():
     m = Model()
     x1 = m.addVar(vtype="B")