Preprocess And/Or constraints

Required for XPRESS (does not like fixed arguments)
ampl · Aug 31, 2023 · 54450d4 · 54450d4
1 parent 668134f
commit 54450d4
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Showing 4 changed files with 69 additions and 6 deletions.
diff --git a/CHANGES.mp.md b/CHANGES.mp.md
@@ -1,6 +1,11 @@
 Summary of recent updates to the AMPL MP Library
 ================================================
 
+## unreleased
+- Check solutions, options sol:chk:*.
+- Preprocess And/Or constraints.
+
+
 ## 20230817
 - Alternative solutions: solve status equal to that
   of the final solution.

diff --git a/include/mp/flat/constr_prepro.h b/include/mp/flat/constr_prepro.h
@@ -21,7 +21,8 @@ namespace mp {
 
 /// A mix-in base class
 /// providing preprocessors of flat constraints.
-/// Currently used before adding a constraint (if not simplified to nothing).
+/// Currently used before adding a constraint
+/// (if not simplified to nothing).
 template <class Impl>
 class ConstraintPreprocessors {
 public:
@@ -271,16 +272,68 @@ class ConstraintPreprocessors {
 
   template <class PreprocessInfo>
   void PreprocessConstraint(
-      AndConstraint& , PreprocessInfo& prepro) {
+      AndConstraint& con, PreprocessInfo& prepro) {
     prepro.narrow_result_bounds(0.0, 1.0);
     prepro.set_result_type( var::INTEGER );
+    // Remove fixed variables for XPRESS (solvers/#61).
+    auto n01 = count_fixed_01(con.GetArguments());
+    if (n01.first) {               // AND = false
+      prepro.narrow_result_bounds(0.0, 0.0);
+      return;
+    }
+    if (con.GetArguments().size() == n01.second) {
+      prepro.narrow_result_bounds(1.0, 1.0);
+      return;
+    }
+    if (n01.second) {
+      std::vector<int> arg1;
+      arg1.reserve(con.GetArguments().size() - n01.second);
+      for (auto x: con.GetArguments()) {
+        if (MPCD( lb(x) ) <= 0.0)    // not fixed
+          arg1.push_back(x);
+      }
+      con.GetArguments() = arg1;
+    }
   }
 
   template <class PreprocessInfo>
   void PreprocessConstraint(
-      OrConstraint& , PreprocessInfo& prepro) {
+      OrConstraint& con, PreprocessInfo& prepro) {
     prepro.narrow_result_bounds(0.0, 1.0);
     prepro.set_result_type( var::INTEGER );
+    // Remove fixed variables for XPRESS (solvers/#61).
+    auto n01 = count_fixed_01(con.GetArguments());
+    if (n01.second) {               // OR = true
+      prepro.narrow_result_bounds(1.0, 1.0);
+      return;
+    }
+    if (con.GetArguments().size() == n01.first) {
+      prepro.narrow_result_bounds(0.0, 0.0);
+      return;
+    }
+    if (n01.first) {
+      std::vector<int> arg1;
+      arg1.reserve(con.GetArguments().size() - n01.first);
+      for (auto x: con.GetArguments()) {
+        if (MPCD( ub(x) ) >= 1.0)    // not fixed
+          arg1.push_back(x);
+      }
+      con.GetArguments() = arg1;
+    }
+  }
+
+  /// Count N fixed binary vars
+  template <class Vec>
+  std::pair<int, int> count_fixed_01(const Vec& vec) const {
+    std::pair<int, int> result {0, 0};
+    for (auto x: vec) {
+      assert(MPCD( is_binary_var(x) ));
+      if (MPCD( ub(x) ) <= 0.0)
+        ++ result.first;
+      if (MPCD( lb(x) ) >= 1.0)
+        ++ result.second;
+    }
+    return result;
   }
 
   template <class PreprocessInfo>

diff --git a/include/mp/flat/converter_model.h b/include/mp/flat/converter_model.h
@@ -147,7 +147,10 @@ class FlatModel
 
   /// Returns true also when fixed
   bool is_binary_var(int v) const {
-    return 0.0<=lb(v) && 1.0>=ub(v) && is_integer_var(v);
+    return
+        (0.0==lb(v) && 1.0==ub(v) && is_integer_var(v))
+        || (is_fixed(v)
+            && (0.0==fixed_value(v) || 1.0==fixed_value(v)));
   }
 
   template <class VarArray=std::initializer_list<int> >

diff --git a/solvers/xpress/xpressmodelapi.cc b/solvers/xpress/xpressmodelapi.cc
@@ -184,8 +184,10 @@ void XpressmpModelAPI::AddConstraint(const SOS2Constraint& sos) {
     (double*)sos.get_weights().data()));
 }
 
-template <class Args, class Params, class NumOrLogic, class Id> void XpressmpModelAPI::addGenCon(
-  const CustomFunctionalConstraint<Args, Params, NumOrLogic, Id>& c, int xpressConType)
+template <class Args, class Params, class NumOrLogic, class Id>
+void XpressmpModelAPI::addGenCon(
+    const CustomFunctionalConstraint<Args, Params, NumOrLogic, Id>& c,
+    int xpressConType)
 {
   int type[] = { xpressConType };
   int resultant[] = { c.GetResultVar() };