From b271d21a4d5433b229aa069098a1fd11ecc959f6 Mon Sep 17 00:00:00 2001
From: Ben Champion <6761956+BenChampion@users.noreply.github.com>
Date: Fri, 29 Nov 2024 14:39:08 +0000
Subject: [PATCH] First draft of Feasibility Jump integration

---
 src/mip/HighsFeasibilityJump.cpp | 91 ++++++++++++++++++++++++++++++--
 1 file changed, 86 insertions(+), 5 deletions(-)

diff --git a/src/mip/HighsFeasibilityJump.cpp b/src/mip/HighsFeasibilityJump.cpp
index 7c31842621..57fb744409 100644
--- a/src/mip/HighsFeasibilityJump.cpp
+++ b/src/mip/HighsFeasibilityJump.cpp
@@ -19,17 +19,98 @@ void HighsMipSolverData::feasibilityJump() {
   printf("HighsMipSolverData::feasibilityJump called with primal bound of %g\n",
          lower_bound);
 
-  // Use feasibility jump to try to find an integer feasible solution
+  const HighsInt MAX_TOTAL_EFFORT = 1e6;
+  const HighsInt MAX_EFFORT_SINCE_LAST_IMPOVEMENT = 1e3;
 
-  const bool found_integer_feasible_solution = false;
-  std::vector<double> col_value;
+  bool found_integer_feasible_solution = false;
+  std::vector<double> col_value(model->num_col_, 0.0);
   double objective_function_value;
 
+  printf("DEBUG: configuring feasilibility jump\n");
+
+  // Configure Feasibility Jump and pass it the problem
+  external_feasibilityjump::equalityTolerance = epsilon;
+  external_feasibilityjump::violationTolerance = feastol;
+
+  auto solver = external_feasibilityjump::FeasibilityJumpSolver();
+
+  printf("DEBUG: adding cols (vars)\n");
+
+  for (int i = 0; i < model->num_col_; ++i) {
+    external_feasibilityjump::VarType fjVarType;
+    if (model->integrality_[i] == HighsVarType::kContinuous) {
+      fjVarType = external_feasibilityjump::VarType::Continuous;
+    } else if (model->integrality_[i] == HighsVarType::kInteger) {
+      fjVarType = external_feasibilityjump::VarType::Integer;
+    } else {
+      printf(
+          "Feasibility Jump only supports continuous and integer variables. "
+          "Skipping Feasibility Jump...\n"
+      );
+      return;
+    }
+    solver.addVar(
+      fjVarType,
+      model->col_lower_[i],
+      model->col_upper_[i],
+      model->col_cost_[i]
+    );
+  }
+
+  printf("DEBUG: adding rows (constraints)\n");
+
+  HighsInt numNzThisRow;
+  HighsInt* rowIndexBuffer = new HighsInt[model->num_col_];
+  double* rowValueBuffer = new double[model->num_col_];
+
+  for (int i = 0; i < model->num_row_; ++i) {
+    bool hasFiniteLower = std::isfinite(model->row_lower_[i]);
+    bool hasFiniteUpper = std::isfinite(model->row_upper_[i]);
+    if (hasFiniteLower || hasFiniteUpper) {
+      model->a_matrix_.getRow(i, numNzThisRow, rowIndexBuffer, rowValueBuffer);
+      // TODO: check if relax_continuous == 1 really is the right thing to pass
+      if (hasFiniteLower) {
+        solver.addConstraint(external_feasibilityjump::RowType::Gte,
+                             model->row_lower_[i], numNzThisRow, rowIndexBuffer,
+                             rowValueBuffer, 1);
+      }
+      if (hasFiniteUpper) {
+        solver.addConstraint(external_feasibilityjump::RowType::Lte,
+                             model->row_upper_[i], numNzThisRow, rowIndexBuffer,
+                             rowValueBuffer, 1);
+      }
+
+    }
+  }
+
+  delete[] rowValueBuffer;
+  delete[] rowIndexBuffer;
+
+  printf("DEBUG: calling Feasibility Jump\n");
+
+  auto fjControlCallback =
+      [=, &col_value, &found_integer_feasible_solution,
+       &objective_function_value](external_feasibilityjump::FJStatus status)
+      -> external_feasibilityjump::CallbackControlFlow {
+    if (std::isfinite(status.solutionObjectiveValue)) {
+      found_integer_feasible_solution = true;
+      col_value = std::vector<double>(status.solution,
+                                      status.solution + status.numVars);
+      objective_function_value = status.solutionObjectiveValue;
+    }
+    if (status.effortSinceLastImprovement > MAX_EFFORT_SINCE_LAST_IMPOVEMENT ||
+        status.totalEffort > MAX_TOTAL_EFFORT) {
+      return external_feasibilityjump::CallbackControlFlow::Terminate;
+    } else {
+      return external_feasibilityjump::CallbackControlFlow::Continue;
+    }
+  };
+
+  solver.solve(col_value.data(), fjControlCallback);
+
   if (found_integer_feasible_solution) {
     // Feasibility jump has found a solution, so call addIncumbent to
     // (possibly) update the incumbent
-    col_value.assign(model->num_col_, 0);
-    objective_function_value = 0.0;
     addIncumbent(col_value, objective_function_value,
                  kSolutionSourceFeasibilityJump);
   }