Port some Hermes-3 finite volume operators

CMakeLists.txt

@@ -376,6 +376,7 @@ if (zoidberg_FOUND EQUAL 0)
 else()
   set(zoidberg_FOUND OFF)
 endif()
+message(STATUS "Found Zoidberg for FCI tests: ${zoidberg_FOUND}")
 
 option(BOUT_GENERATE_FIELDOPS "Automatically re-generate the Field arithmetic operators from the Python templates. \
 Requires Python3, clang-format, and Jinja2. Turn this OFF to skip generating them if, for example, \

include/bout/difops.hxx

@@ -40,7 +40,9 @@
 #include "bout/field3d.hxx"
 
 #include "bout/bout_types.hxx"
-#include "bout/solver.hxx"
+#include "bout/coordinates.hxx"
+
+class Solver;
 
 /*!
  * Parallel derivative (central differencing) in Y
@@ -193,6 +195,10 @@ Field3D Div_par_K_Grad_par(const Field3D& kY, const Field2D& f,
 Field3D Div_par_K_Grad_par(const Field3D& kY, const Field3D& f,
                            CELL_LOC outloc = CELL_DEFAULT);
 
+/// Version with energy flow diagnostic
+Field3D Div_par_K_Grad_par_mod(const Field3D& k, const Field3D& f, Field3D& flow_ylow,
+                               bool bndry_flux = true);
+
 /*!
  * Perpendicular Laplacian operator
  *