Made Residual struct definition public, and documented.

This is in anticipation of implementing CPR preconditioning.

opm/autodiff/FullyImplicitBlackoilSolver.hpp

@@ -78,9 +78,45 @@ namespace Opm {
              BlackoilState& state ,
              WellState&     wstate);
 
+        /// Typedef used throughout the solver, in the public section
+        /// since it is used in the definition of Residual.
+        typedef AutoDiffBlock<double> ADB;
+
+        /// Residual structure of the fully implicit solver.
+        /// All equations are given as AD types, with multiple
+        /// jacobian blocks corresponding to the primary unknowns. The
+        /// primary unknowns are for a three-phase simulation, in order:
+        ///    p    (pressure)
+        ///    sw   (water saturation)
+        ///    xvar (gas saturation, gas-oil ratio or oil-gas ratio)
+        ///    qs   (well outflows by well and phase)
+        ///    bhp  (bottom hole pressures)
+        /// In the above, the xvar variable will have a different
+        /// meaning from cell to cell, corresponding to the state in
+        /// that cell (saturated, undersaturated oil or undersaturated
+        /// gas). In a two-phase simulation, either sw or xvar is not
+        /// used, depending on which face is missing.
+        struct Residual {
+            /// The mass_balance vector has one element for each
+            /// active phase, each of which has size equal to the
+            /// number of cells. Each mass balance equation is given
+            /// in terms of surface volumes.
+            std::vector<ADB> mass_balance;
+            /// The well_flux_eq has size equal to the number of wells
+            /// times the number of phases. It contains the well flow
+            /// equations, relating the total well flows to
+            /// bottom-hole pressures and reservoir conditions.
+            ADB well_flux_eq;
+            /// The well_eq has size equal to the number of wells. It
+            /// contains the well control equations, that is for each
+            /// well either a rate specification or bottom hole
+            /// pressure specification.
+            ADB well_eq;
+        };
+
+
     private:
         // Types and enums
-        typedef AutoDiffBlock<double> ADB;
         typedef ADB::V V;
         typedef ADB::M M;
         typedef Eigen::Array<double,
@@ -136,14 +172,7 @@ namespace Opm {
         std::vector<ReservoirResidualQuant> rq_;
         std::vector<PhasePresence> phaseCondition_;
 
-        // The mass_balance vector has one element for each active phase,
-        // each of which has size equal to the number of cells.
-        // The well_eq has size equal to the number of wells.
-        struct {
-            std::vector<ADB> mass_balance;
-            ADB well_flux_eq;
-            ADB well_eq;
-        } residual_;
+        Residual residual_;
 
         // Private methods.
         SolutionState