Use references for inline functions for performance

Author: EmilyBourne

src/Residual/ResidualGive/applyAGive.cpp

@@ -3,7 +3,7 @@
 #include "../../../include/common/geometry_helper.h"
 
 inline void node_apply_a_give(int i_r, int i_theta, double r, double theta, const PolarGrid& grid, const LevelCache& level_cache, bool DirBC_Interior,
-                              Vector<double> result, ConstVector<double> x)
+                              Vector<double>& result, ConstVector<double>& x)
 {
     const int global_index = grid.index(i_r, i_theta);
     double coeff_beta, arr, att, art, detDF;

src/Residual/ResidualTake/applyResidualTake.cpp

@@ -1,9 +1,9 @@
 #include "../../../include/Residual/ResidualTake/residualTake.h"
 
 inline void node_apply_residual_take(int i_r, int i_theta, const PolarGrid& grid, bool DirBC_Interior,
-                                     Vector<double> result, ConstVector<double> rhs, ConstVector<double> x,
-                                     ConstVector<double> arr, ConstVector<double> att, ConstVector<double> art,
-                                     ConstVector<double> detDF, ConstVector<double> coeff_beta)
+                                     Vector<double>& result, ConstVector<double>& rhs, ConstVector<double>& x,
+                                     ConstVector<double>& arr, ConstVector<double>& att, ConstVector<double>& art,
+                                     ConstVector<double>& detDF, ConstVector<double>& coeff_beta)
 {
     do {
         /* -------------------- */