Speed up glop in CP-SAT

ortools/glop/revised_simplex.cc

@@ -269,12 +269,7 @@ Status RevisedSimplex::Solve(const LinearProgram& lp, TimeLimit* time_limit) {
     //
     // Note(user): Currently, we never do both at the same time, so we could
     // be a bit faster here, but then this is quick anyway.
-    const VariableStatusRow& statuses = variables_info_.GetStatusRow();
-    for (ColIndex col(0); col < num_cols_; ++col) {
-      if (statuses[col] != VariableStatus::BASIC) {
-        SetNonBasicVariableStatusAndDeriveValue(col, statuses[col]);
-      }
-    }
+    variable_values_.ResetAllNonBasicVariableValues();
     GLOP_RETURN_IF_ERROR(basis_factorization_.Refactorize());
     PermuteBasis();
     variable_values_.RecomputeBasicVariableValues();
@@ -895,7 +890,7 @@ void RevisedSimplex::InitializeVariableStatusesForWarmStart(
       if (num_basic_variables == num_rows_) {
         VLOG(1) << "Too many basic variables in the warm-start basis."
                 << "Only keeping the first ones as VariableStatus::BASIC.";
-        SetNonBasicVariableStatusAndDeriveValue(col, default_status);
+        variables_info_.UpdateToNonBasicStatus(col, default_status);
       } else {
         ++num_basic_variables;
         variables_info_.UpdateToBasicStatus(col);
@@ -914,9 +909,12 @@ void RevisedSimplex::InitializeVariableStatusesForWarmStart(
             upper_bound_[col] == kInfinity))) {
         status = default_status;
       }
-      SetNonBasicVariableStatusAndDeriveValue(col, status);
+      variables_info_.UpdateToNonBasicStatus(col, status);
     }
   }
+
+  // Initialize the values.
+  variable_values_.ResetAllNonBasicVariableValues();
 }
 
 // This implementation starts with an initial matrix B equal to the identity

ortools/glop/variable_values.cc

@@ -62,6 +62,31 @@ void VariableValues::SetNonBasicVariableValueFromStatus(ColIndex col) {
   // get a compile-time error if a value is missing.
 }
 
+void VariableValues::ResetAllNonBasicVariableValues() {
+  const DenseRow& lower_bounds = variables_info_.GetVariableLowerBounds();
+  const DenseRow& upper_bounds = variables_info_.GetVariableUpperBounds();
+  const VariableStatusRow& statuses = variables_info_.GetStatusRow();
+  const ColIndex num_cols = matrix_.num_cols();
+  variable_values_.resize(num_cols, 0.0);
+  for (ColIndex col(0); col < num_cols; ++col) {
+    switch (statuses[col]) {
+      case VariableStatus::FIXED_VALUE:
+        ABSL_FALLTHROUGH_INTENDED;
+      case VariableStatus::AT_LOWER_BOUND:
+        variable_values_[col] = lower_bounds[col];
+        break;
+      case VariableStatus::AT_UPPER_BOUND:
+        variable_values_[col] = upper_bounds[col];
+        break;
+      case VariableStatus::FREE:
+        variable_values_[col] = 0.0;
+        break;
+      case VariableStatus::BASIC:
+        break;
+    }
+  }
+}
+
 void VariableValues::RecomputeBasicVariableValues() {
   SCOPED_TIME_STAT(&stats_);
   DCHECK(basis_factorization_.IsRefactorized());

ortools/glop/variable_values.h

@@ -52,6 +52,9 @@ class VariableValues {
   // function and it is up to the client to call RecomputeBasicVariableValues().
   void SetNonBasicVariableValueFromStatus(ColIndex col);
 
+  // Calls SetNonBasicVariableValueFromStatus() on all non-basic variables.
+  void ResetAllNonBasicVariableValues();
+
   // Recomputes the value of the basic variables from the non-basic ones knowing
   // that the linear program matrix A times the variable values vector must be
   // zero. It is better to call this when the basis is refactorized. This