From 4007aa885f87e25e3db558db1fc388fb6772b9ad Mon Sep 17 00:00:00 2001
From: Laurent Perron <lperron@google.com>
Date: Wed, 25 Jul 2018 10:21:35 -0700
Subject: [PATCH] simplify glop code

---
 ortools/glop/entering_variable.cc | 11 ++++-------
 ortools/glop/entering_variable.h  |  6 ++----
 ortools/glop/revised_simplex.cc   |  6 +++---
 3 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/ortools/glop/entering_variable.cc b/ortools/glop/entering_variable.cc
index 84359dc905..bf1f6f31b5 100644
--- a/ortools/glop/entering_variable.cc
+++ b/ortools/glop/entering_variable.cc
@@ -89,9 +89,9 @@ Status EnteringVariable::PrimalChooseEnteringColumn(ColIndex* entering_col) {
 Status EnteringVariable::DualChooseEnteringColumn(
     const UpdateRow& update_row, Fractional cost_variation,
     std::vector<ColIndex>* bound_flip_candidates, ColIndex* entering_col,
-    Fractional* pivot, Fractional* step) {
+    Fractional* step) {
   GLOP_RETURN_ERROR_IF_NULL(entering_col);
-  GLOP_RETURN_ERROR_IF_NULL(pivot);
+  GLOP_RETURN_ERROR_IF_NULL(step);
   const DenseRow& update_coefficient = update_row.GetCoefficients();
   const DenseRow& reduced_costs = reduced_costs_->GetReducedCosts();
   SCOPED_TIME_STAT(&stats_);
@@ -241,7 +241,6 @@ Status EnteringVariable::DualChooseEnteringColumn(
   }
 
   if (*entering_col == kInvalidCol) return Status::OK();
-  *pivot = update_coefficient[*entering_col];
 
   // If the step is 0.0, we make sure the reduced cost is 0.0 so
   // UpdateReducedCosts() will not take a step that goes in the wrong way (a few
@@ -266,9 +265,9 @@ Status EnteringVariable::DualChooseEnteringColumn(
 
 Status EnteringVariable::DualPhaseIChooseEnteringColumn(
     const UpdateRow& update_row, Fractional cost_variation,
-    ColIndex* entering_col, Fractional* pivot, Fractional* step) {
+    ColIndex* entering_col, Fractional* step) {
   GLOP_RETURN_ERROR_IF_NULL(entering_col);
-  GLOP_RETURN_ERROR_IF_NULL(pivot);
+  GLOP_RETURN_ERROR_IF_NULL(step);
   const DenseRow& update_coefficient = update_row.GetCoefficients();
   const DenseRow& reduced_costs = reduced_costs_->GetReducedCosts();
   SCOPED_TIME_STAT(&stats_);
@@ -365,8 +364,6 @@ Status EnteringVariable::DualPhaseIChooseEnteringColumn(
     std::pop_heap(breakpoints_.begin(), breakpoints_.end());
     breakpoints_.pop_back();
   }
-  *pivot =
-      (*entering_col == kInvalidCol) ? 0.0 : update_coefficient[*entering_col];
   return Status::OK();
 }
 
diff --git a/ortools/glop/entering_variable.h b/ortools/glop/entering_variable.h
index 3872981b72..9bbc3829dc 100644
--- a/ortools/glop/entering_variable.h
+++ b/ortools/glop/entering_variable.h
@@ -67,12 +67,11 @@ class EnteringVariable {
   // Returns the index of the entering column given that we want to move along
   // the "update" row vector in the direction given by the sign of
   // cost_variation. Computes the smallest step that keeps the dual feasibility
-  // for all the columns. The pivot is the coefficient of the "update" vector at
-  // the entering column index.
+  // for all the columns.
   Status DualChooseEnteringColumn(const UpdateRow& update_row,
                                   Fractional cost_variation,
                                   std::vector<ColIndex>* bound_flip_candidates,
-                                  ColIndex* entering_col, Fractional* pivot,
+                                  ColIndex* entering_col,
                                   Fractional* step) MUST_USE_RESULT;
 
   // Dual feasibility phase (i.e. phase I) ratio test.
@@ -82,7 +81,6 @@ class EnteringVariable {
   Status DualPhaseIChooseEnteringColumn(const UpdateRow& update_row,
                                         Fractional cost_variation,
                                         ColIndex* entering_col,
-                                        Fractional* pivot,
                                         Fractional* step) MUST_USE_RESULT;
 
   // Sets the pricing parameters. This does not change the pricing rule.
diff --git a/ortools/glop/revised_simplex.cc b/ortools/glop/revised_simplex.cc
index f1a9df7014..57210ba12b 100644
--- a/ortools/glop/revised_simplex.cc
+++ b/ortools/glop/revised_simplex.cc
@@ -2553,7 +2553,6 @@ Status RevisedSimplex::DualMinimize(TimeLimit* time_limit) {
 
   // Entering variable.
   ColIndex entering_col;
-  Fractional entering_coeff;
   Fractional ratio;
 
   while (true) {
@@ -2670,11 +2669,11 @@ Status RevisedSimplex::DualMinimize(TimeLimit* time_limit) {
     update_row_.ComputeUpdateRow(leaving_row);
     if (feasibility_phase_) {
       GLOP_RETURN_IF_ERROR(entering_variable_.DualPhaseIChooseEnteringColumn(
-          update_row_, cost_variation, &entering_col, &entering_coeff, &ratio));
+          update_row_, cost_variation, &entering_col, &ratio));
     } else {
       GLOP_RETURN_IF_ERROR(entering_variable_.DualChooseEnteringColumn(
           update_row_, cost_variation, &bound_flip_candidates, &entering_col,
-          &entering_coeff, &ratio));
+          &ratio));
     }
 
     // No entering_col: Unbounded problem / Infeasible problem.
@@ -2708,6 +2707,7 @@ Status RevisedSimplex::DualMinimize(TimeLimit* time_limit) {
     }
 
     // If the coefficient is too small, we recompute the reduced costs.
+    const Fractional entering_coeff = update_row_.GetCoefficient(entering_col);
     if (std::abs(entering_coeff) < parameters_.dual_small_pivot_threshold() &&
         !reduced_costs_.AreReducedCostsPrecise()) {
       VLOG(1) << "Trying not to pivot by " << entering_coeff;