Revert: Removed unused SimulatorState comparison.

This reverts commit 5ce1d84ac1.

opm/core/simulator/SimulatorState.cpp

@@ -6,6 +6,40 @@
 
 using namespace Opm;
 
+bool
+SimulatorState::equals (const SimulatorState& other,
+                        double epsilon) const {
+    bool equal = (num_phases_ == other.num_phases_);
+
+    // if we use &=, then all the tests will be run regardless
+    equal = equal && vectorApproxEqual( pressure() , other.pressure() , epsilon);
+    equal = equal && vectorApproxEqual( temperature() , other.temperature() , epsilon);
+    equal = equal && vectorApproxEqual( facepressure() , other.facepressure() , epsilon);
+    equal = equal && vectorApproxEqual( faceflux() , other.faceflux() , epsilon);
+    equal = equal && vectorApproxEqual( saturation() , other.saturation() , epsilon);
+
+    return equal;
+}
+
+bool
+SimulatorState::vectorApproxEqual(const std::vector<double>& v1,
+                                  const std::vector<double>& v2,
+                                  double epsilon) {
+    if (v1.size() != v2.size()) {
+        return false;
+    }
+
+    for (size_t i = 0; i < v1.size(); i++) {
+        const double diff = std::abs(v1[i] - v2[i]);
+        const double scale = std::abs(v1[i]) + std::abs(v2[i]);
+        if (diff > epsilon * scale) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
 
 void
 SimulatorState::init(int number_of_cells, int number_of_faces, int num_phases)

opm/core/simulator/SimulatorState.hpp

@@ -61,6 +61,13 @@ namespace Opm
         const std::vector<double>& faceflux    () const { return faceData_[ faceFluxId_ ];        }
         const std::vector<double>& saturation  () const { return cellData_[ saturationId_ ];  }
 
+        /**
+         * Compare this state with another, to see if they are different
+         * only within a small margin.
+         */
+        virtual bool equals(const SimulatorState& other,
+                            double epsilon = 1e-8) const;
+
         std::vector< std::vector<double> >& cellData() { return cellData_; }
         const std::vector< std::vector<double> >& cellData() const { return cellData_; }
 
@@ -87,6 +94,19 @@ namespace Opm
         /// \brief names for the face data
         std::vector< std::string > faceDataNames_;
 
+    protected:
+        /**
+         * Check if two vectors are equal within a margin.
+         *
+         * @param epsilon Relative difference that is tolerated for the
+         *                vectors to still be considered equal.
+         *
+         * @return True if every element is within the margin, false if
+         *         there is at least one that is not.
+         */
+        static bool vectorApproxEqual(const std::vector<double>& v1,
+                                      const std::vector<double>& v2,
+                                      double epsilon);
     };
 
 } // namespace Opm