Port some Hermes-3 finite volume operators (rebased)

CMakeLists.txt

@@ -140,6 +140,7 @@ set(BOUT_SOURCES
     ./include/bout/fieldgroup.hxx
     ./include/bout/fieldperp.hxx
     ./include/bout/fv_ops.hxx
+    ./include/bout/fv_ops_impl.hxx
     ./include/bout/generic_factory.hxx
     ./include/bout/globalfield.hxx
     ./include/bout/globalindexer.hxx

include/bout/coordinates.hxx

@@ -1,15 +1,8 @@
 /**************************************************************************
  * Describes coordinate systems
  *
- * ChangeLog
- * =========
- *
- * 2014-11-10 Ben Dudson <bd512@york.ac.uk>
- *    * Created by separating metric from Mesh
- *
- *
  **************************************************************************
- * Copyright 2014-2025 BOUT++ contributors
+ * Copyright 2014-2026 BOUT++ contributors
  *
  * Contact: Ben Dudson, dudson2@llnl.gov
  *
@@ -116,101 +109,115 @@ public:
   FieldMetric& g_22_yhigh();
   // Cell Areas
   const FieldMetric& cell_area_xlow() const {
-    if (!_cell_area_xlow.has_value()) {
-      _compute_cell_area_x();
+    if (_cell_area_xlow.has_value()) {
+      return *_cell_area_xlow;
     }
+    _compute_cell_area_x();
     ASSERT2(_cell_area_xlow.has_value());
     return *_cell_area_xlow;
   }
   const FieldMetric& cell_area_xhigh() const {
-    if (!_cell_area_xhigh.has_value()) {
-      _compute_cell_area_x();
+    if (_cell_area_xhigh.has_value()) {
+      return *_cell_area_xhigh;
     }
+    _compute_cell_area_x();
     ASSERT2(_cell_area_xhigh.has_value());
     return *_cell_area_xhigh;
   }
   const FieldMetric& cell_area_ylow() const {
-    if (!_cell_area_ylow.has_value()) {
-      _compute_cell_area_y();
+    if (_cell_area_ylow.has_value()) {
+      return *_cell_area_ylow;
     }
+    _compute_cell_area_y();
     ASSERT2(_cell_area_ylow.has_value());
     return *_cell_area_ylow;
   }
   const FieldMetric& cell_area_yhigh() const {
-    if (!_cell_area_yhigh.has_value()) {
-      _compute_cell_area_y();
+    if (_cell_area_yhigh.has_value()) {
+      return *_cell_area_yhigh;
     }
+    _compute_cell_area_y();
     ASSERT2(_cell_area_yhigh.has_value());
     return *_cell_area_yhigh;
   }
   const FieldMetric& cell_area_zlow() const {
-    if (!_cell_area_zlow.has_value()) {
-      _compute_cell_area_z();
+    if (_cell_area_zlow.has_value()) {
+      return *_cell_area_zlow;
     }
+    _compute_cell_area_z();
     ASSERT2(_cell_area_zlow.has_value());
     return *_cell_area_zlow;
   }
   const FieldMetric& cell_area_zhigh() const {
-    if (!_cell_area_zhigh.has_value()) {
-      _compute_cell_area_z();
+    if (_cell_area_zhigh.has_value()) {
+      return *_cell_area_zhigh;
     }
+    _compute_cell_area_z();
     ASSERT2(_cell_area_zhigh.has_value());
     return *_cell_area_zhigh;
   }
   FieldMetric& cell_area_xlow() {
-    if (!_cell_area_xlow.has_value()) {
-      _compute_cell_area_x();
+    if (_cell_area_xlow.has_value()) {
+      return *_cell_area_xlow;
     }
+    _compute_cell_area_x();
     ASSERT2(_cell_area_xlow.has_value());
     return *_cell_area_xlow;
   }
   FieldMetric& cell_area_xhigh() {
-    if (!_cell_area_xhigh.has_value()) {
-      _compute_cell_area_x();
+    if (_cell_area_xhigh.has_value()) {
+      return *_cell_area_xhigh;
     }
+    _compute_cell_area_x();
     ASSERT2(_cell_area_xhigh.has_value());
     return *_cell_area_xhigh;
   }
   FieldMetric& cell_area_ylow() {
-    if (!_cell_area_ylow.has_value()) {
-      _compute_cell_area_y();
+    if (_cell_area_ylow.has_value()) {
+      return *_cell_area_ylow;
     }
+    _compute_cell_area_y();
     ASSERT2(_cell_area_ylow.has_value());
     return *_cell_area_ylow;
   }
   FieldMetric& cell_area_yhigh() {
-    if (!_cell_area_yhigh.has_value()) {
-      _compute_cell_area_y();
+    if (_cell_area_yhigh.has_value()) {
+      return *_cell_area_yhigh;
     }
+    _compute_cell_area_y();
     ASSERT2(_cell_area_yhigh.has_value());
     return *_cell_area_yhigh;
   }
   FieldMetric& cell_area_zlow() {
-    if (!_cell_area_zlow.has_value()) {
-      _compute_cell_area_z();
+    if (_cell_area_zlow.has_value()) {
+      return *_cell_area_zlow;
     }
+    _compute_cell_area_z();
     ASSERT2(_cell_area_zlow.has_value());
     return *_cell_area_zlow;
   }
   FieldMetric& cell_area_zhigh() {
-    if (!_cell_area_zhigh.has_value()) {
-      _compute_cell_area_z();
+    if (_cell_area_zhigh.has_value()) {
+      return *_cell_area_zhigh;
     }
+    _compute_cell_area_z();
     ASSERT2(_cell_area_zhigh.has_value());
     return *_cell_area_zhigh;
   }
   // Cell Volume
   const FieldMetric& cell_volume() const {
-    if (!_cell_volume.has_value()) {
-      _compute_cell_volume();
+    if (_cell_volume.has_value()) {
+      return *_cell_volume;
     }
+    _compute_cell_volume();
     ASSERT2(_cell_volume.has_value());
     return *_cell_volume;
   }
   FieldMetric& cell_volume() {
-    if (!_cell_volume.has_value()) {
-      _compute_cell_volume();
+    if (_cell_volume.has_value()) {
+      return *_cell_volume;
     }
+    _compute_cell_volume();
     ASSERT2(_cell_volume.has_value());
     return *_cell_volume;
   }

include/bout/derivs.hxx

@@ -35,6 +35,7 @@
 #include "bout/vector3d.hxx"
 
 #include "bout/bout_types.hxx"
+#include <type_traits>
 
 ////////// FIRST DERIVATIVES //////////
 
@@ -86,6 +87,13 @@ Field3D DDY(const Field3DParallel& f, CELL_LOC outloc = CELL_DEFAULT,
             const std::string& method = "DEFAULT",
             const std::string& region = "RGN_NOBNDRY");
 
+template <typename E>
+std::enable_if_t<is_expr_field3d_v<E> && !bout::utils::is_Field3D_v<E>, const Field3D>
+DDY(const E& expr, CELL_LOC outloc = CELL_DEFAULT, const std::string& method = "DEFAULT",
+    const std::string& region = "RGN_NOBNDRY") {
+  return DDY(Field3D{expr}, outloc, method, region);
+}
+
 /// Calculate first partial derivative in Y
 ///
 ///   \f$\partial / \partial y\f$

include/bout/difops.hxx

@@ -1,11 +1,11 @@
 /*!******************************************************************************
  * \file difops.hxx
- * 
+ *
  * Differential operators
  *
  * Changelog:
  *
- * 2009-01 Ben Dudson <bd512@york.ac.uk> 
+ * 2009-01 Ben Dudson <bd512@york.ac.uk>
  *    * Added two optional parameters which can be put in any order
  *      These determine the method to use (DIFF_METHOD)
  *      and CELL_LOC location of the result.
@@ -15,7 +15,7 @@
  * Copyright 2010 B.D.Dudson, S.Farley, M.V.Umansky, X.Q.Xu
  *
  * Contact: Ben Dudson, bd512@york.ac.uk
- * 
+ *
  * This file is part of BOUT++.
  *
  * BOUT++ is free software: you can redistribute it and/or modify
@@ -30,7 +30,7 @@
  *
  * You should have received a copy of the GNU Lesser General Public License
  * along with BOUT++.  If not, see <http://www.gnu.org/licenses/>.
- * 
+ *
  *******************************************************************************/
 
 #ifndef BOUT_DIFOPS_H
@@ -81,7 +81,7 @@ Field3D Grad_parP(const Field3D& apar, const Field3D& f);
  * \f[
  *    v\mathbf{b}_0 \cdot \nabla f
  * \f]
- * 
+ *
  *
  * @param[in] v  The velocity in y direction
  * @param[in] f  The scalar field to be differentiated
@@ -175,7 +175,7 @@ inline Field3D Grad2_par2(const Field3D& f, CELL_LOC outloc, DIFF_METHOD method)
 
 /*!
  * Parallel divergence of diffusive flux, K*Grad_par
- * 
+ *
  * \f[
  *    \nabla \cdot ( \mathbf{b}_0 kY (\mathbf{b}_0 \cdot \nabla) f )
  * \f]
@@ -195,12 +195,17 @@ 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
+/// For FCI fields, `flow_ylow` is currently returned as zero.
+Field3D Div_par_K_Grad_par_mod(const Field3D& k, const Field3D& f, Field3D& flow_ylow,
+                               bool bndry_flux = true);
+
 /*!
  * Perpendicular Laplacian operator
  *
  * This version only includes terms in X and Z, dropping
- * derivatives in Y. This is the inverse operation to 
- * the Laplacian inversion class. 
+ * derivatives in Y. This is the inverse operation to
+ * the Laplacian inversion class.
  *
  * For the full perpendicular Laplacian, use Laplace_perp
  */
@@ -212,7 +217,7 @@ FieldPerp Delp2(const FieldPerp& f, CELL_LOC outloc = CELL_DEFAULT, bool useFFT
 /*!
  * Perpendicular Laplacian, keeping y derivatives
  *
- * 
+ *
  */
 Coordinates::FieldMetric
 Laplace_perp(const Field2D& f, CELL_LOC outloc = CELL_DEFAULT,
@@ -246,18 +251,18 @@ Field2D Laplace_perpXY(const Field2D& A, const Field2D& f);
 
 /*!
  * Terms of form b0 x Grad(phi) dot Grad(A)
- * 
+ *
  */
 Coordinates::FieldMetric b0xGrad_dot_Grad(const Field2D& phi, const Field2D& A,
                                           CELL_LOC outloc = CELL_DEFAULT);
 
 /*!
- * Terms of form 
+ * Terms of form
  *
  * \f[
  *   \mathbf{b}_0 \times \nabla \phi \cdot \nabla A
  * \f]
- * 
+ *
  * @param[in] phi The scalar potential
  * @param[in] A   The field being advected
  * @param[in] outloc  The cell location where the result is defined. By default the same as A.
@@ -291,13 +296,13 @@ constexpr BRACKET_METHOD BRACKET_CTU = BRACKET_METHOD::ctu;
  * \f[
  *   [f, g] = (1/B) \mathbf{b}_0 \times \nabla f  \cdot \nabla g
  * \f]
- * 
+ *
  * @param[in] f  The potential
  * @param[in] g  The field being advected
  * @param[in] method   The method to use
  * @param[in] outloc   The cell location where the result is defined. Default is the same as g
  * @param[in] solver   Pointer to the time integration solver
- * 
+ *
  */
 Coordinates::FieldMetric bracket(const Field2D& f, const Field2D& g,
                                  BRACKET_METHOD method = BRACKET_STD,