Enable different boundary conditions for different fields on different boundaries

data/boundary-composition/ascii-data/test/box_3d_2fields_back.0.txt

@@ -0,0 +1,13 @@
+# Test data for ascii data boundary composition.
+# Only next line is parsed in format: [nx] [ny] because of keyword "POINTS:"
+# POINTS: 3 3
+# Columns: x y composition_1 composition_2.
+0.      0.      0. 0.
+330000. 0.      0. 0.
+660000. 0.      0. 0.
+0.      330000. 1. 1.
+330000. 330000. 1. 1.
+660000. 330000. 1. 1.
+0.      660000. 0. 0.
+330000. 660000. 0. 0.
+660000. 660000. 0. 0.

data/boundary-composition/ascii-data/test/box_3d_2fields_bottom.0.txt

@@ -0,0 +1,13 @@
+# Test data for ascii data boundary composition.
+# Only next line is parsed in format: [nx] [ny] because of keyword "POINTS:"
+# POINTS: 3 3
+# Columns: x z composition_1 composition_2.
+0.      0.      0. 0.
+330000. 0.      0. 0.
+660000. 0.      0. 0.
+0.      330000. 1. 1.
+330000. 330000. 1. 1.
+660000. 330000. 1. 1.
+0.      660000. 0. 0.
+330000. 660000. 0. 0.
+660000. 660000. 0. 0.

data/boundary-composition/ascii-data/test/box_3d_2fields_front.0.txt

@@ -0,0 +1,13 @@
+# Test data for ascii data boundary composition.
+# Only next line is parsed in format: [nx] [ny] because of keyword "POINTS:"
+# POINTS: 3 3
+# Columns: x y composition_1 composition_2.
+0.      0.      0. 0.
+330000. 0.      0. 0.
+660000. 0.      0. 0.
+0.      330000. 1. 1.
+330000. 330000. 1. 1.
+660000. 330000. 1. 1.
+0.      660000. 0. 0.
+330000. 660000. 0. 0.
+660000. 660000. 0. 0.

data/boundary-composition/ascii-data/test/box_3d_2fields_left.0.txt

@@ -0,0 +1,13 @@
+# Test data for ascii data boundary composition.
+# Only next line is parsed in format: [nx] [ny] because of keyword "POINTS:"
+# POINTS: 3 3
+# Columns: x z composition_1 composition_2.
+0.      0.      0. 0.
+330000. 0.      1. 1.
+660000. 0.      0. 0.
+0.      330000. 1. 1.
+330000. 330000. 1. 1.
+660000. 330000. 1. 1.
+0.      660000. 0. 0.
+330000. 660000. 1. 1.
+660000. 660000. 0. 0.

data/boundary-composition/ascii-data/test/box_3d_2fields_top.0.txt

@@ -0,0 +1,13 @@
+# Test data for ascii data boundary composition.
+# Only next line is parsed in format: [nx] [ny] because of keyword "POINTS:"
+# POINTS: 3 3
+# Columns: x z composition_1 composition_2.
+0.      0.      0. 0.
+330000. 0.      0. 0.
+660000. 0.      0. 0.
+0.      330000. 1. 1.
+330000. 330000. 1. 1.
+660000. 330000. 1. 1.
+0.      660000. 0. 0.
+330000. 660000. 0. 0.
+660000. 660000. 0. 0.

doc/modules/changes/20260511_glerum

@@ -0,0 +1,7 @@
+ New: It is now possible to specify different boundary
+ composition plugins for different fields on different
+ boundaries. This means that not all fields need to be
+ prescribed and two prescribed fields can use different
+ plugins to compute the boundary composition.
+ <br>
+ (Anne Glerum 2026/05/11)

include/aspect/boundary_composition/interface.h

@@ -212,6 +212,57 @@ namespace aspect
         bool
         allows_fixed_composition_on_outflow_boundaries() const;
 
+        /*
+         * Return whether on the given boundary the given field
+         * is fixed.
+         */
+        bool
+        field_is_fixed_on_boundary(const types::boundary_id boundary_id,
+                                   const unsigned int compositional_field) const;
+
+        /*
+         * Return whether there are boundaries where only a subset
+         * of the compositional fields is prescribed. If false,
+         * either there are no fixed boundary compositions, or all fields
+         * are fixed on the fixed composition boundaries.
+         */
+        bool
+        boundaries_with_fixed_subset_of_fields_exist() const;
+
+        /*
+         * Return a list of fields that are fixed on the given boundary.
+         */
+        std::vector<unsigned int>
+        get_fixed_fields_on_boundary (const types::boundary_id boundary_id) const;
+
+        /*
+         * Return a set of boundary indicators on which the given field
+         * is fixed.
+         */
+        std::set<types::boundary_id>
+        get_fixed_boundaries_for_field (const unsigned int compositional_field) const;
+
+        /*
+         * Return the set of compositional fields that are fixed
+         * for the given plugin name.
+         */
+        std::set<unsigned int>
+        get_fixed_compositional_fields_for_plugin (const std::string plugin_name) const;
+
+        /*
+         * Return the set of compositional fields that are fixed
+         * for the given plugin name.
+         */
+        std::set<unsigned int>
+        get_fixed_compositional_fields_for_plugin_on_boundary (const std::string plugin_name, const types::boundary_id boundary_id) const;
+
+        /*
+         * Return the set of boundary indicators for which fields are fixed
+         * for the given plugin name.
+         */
+        std::set<types::boundary_id>
+        get_fixed_composition_boundaries_for_plugin (const std::string plugin_name) const;
+
         /**
          * For the current plugin subsystem, write a connection graph of all of the
          * plugins we know about, in the format that the
@@ -235,25 +286,60 @@ namespace aspect
                         << arg1
                         << "> among the names of registered boundary composition objects.");
       private:
+
+        /**
+         * A list of boundary indicators that indicate for
+         * each plugin in the list of plugin_objects which boundary ids
+         * it is responsible for. By default each plugin
+         * is active for all boundaries, but this list
+         * can be modified from the input file and by
+         * derived classes to limit the application
+         * of plugins to specific boundaries.
+         */
+        std::vector <std::vector<types::boundary_id>> boundary_indicators;
+
         /**
-         * A list of enums of boundary composition operators that have been
+         * A list of masks that specify for each plugin object
+         * for each boundary it applies to which compositional fields
+         *  are prescribed (true) and which are not (false).
+         */
+        std::vector <std::vector<ComponentMask>> masks_fields;
+
+        /**
+         * A list of enums of boundary composition operators for each
+         * boundary indicator associated with a boundary composition plugin that has been
          * requested in the parameter file. Each name is associated
          * with a model_name, and is used to modify the composition
          * boundary with the values from the current plugin.
          */
-        std::vector<aspect::Utilities::Operator> model_operators;
+        std::vector <std::vector<aspect::Utilities::Operator>> model_operators;
 
         /**
          * A set of boundary ids on which the boundary_composition_objects
-         * will be applied.
+         * will be applied. This set does not distinguish between boundaries
+         * on which only a subset of the fields are fixed and boundaries on
+         * which all fields are fixed. Any boundary with at least one fixed
+         * field is included.
          */
         std::set<types::boundary_id> fixed_composition_boundary_indicators;
 
+        /**
+         * A set of compositional field numbers that are fixed on any of the
+         * boundaries, i.e. potentially a subset of n_compositional_fields.
+         */
+        std::set<unsigned int> fixed_compositional_fields;
+
         /**
          * Whether we allow the composition to be fixed on parts of the boundary
          * where material flows out of the domain.
          */
         bool allow_fixed_composition_on_outflow_boundaries;
+
+        /**
+         * Whether one or more boundaries only have fixed boundary conditions
+         * for a subset of fields, instead of all fields.
+         */
+        bool do_boundaries_with_fixed_subset_of_fields_exist = false;
     };
 
 

source/boundary_composition/ascii_data.cc

@@ -37,8 +37,10 @@ namespace aspect
     void
     AsciiData<dim>::initialize ()
     {
-      Utilities::AsciiDataBoundary<dim>::initialize(this->get_fixed_composition_boundary_indicators(),
-                                                    this->n_compositional_fields());
+      const unsigned int n_fixed_fields = this->get_boundary_composition_manager().get_fixed_compositional_fields_for_plugin("ascii data").size();
+      const std::set<types::boundary_id> fixed_boundary_indicators = this->get_boundary_composition_manager().get_fixed_composition_boundaries_for_plugin("ascii data");
+      Utilities::AsciiDataBoundary<dim>::initialize(fixed_boundary_indicators,
+                                                    n_fixed_fields);
     }
 
 
@@ -59,9 +61,24 @@ namespace aspect
                           const Point<dim> &position,
                           const unsigned int compositional_field) const
     {
+      // In case not all fields are fixed on the boundary,
+      // figure out the right index of the given field.
+      unsigned int field_id = compositional_field;
+      if (this->get_boundary_composition_manager().boundaries_with_fixed_subset_of_fields_exist())
+        {
+          const std::set<unsigned int> fixed_fields = this->get_boundary_composition_manager().get_fixed_compositional_fields_for_plugin("ascii data");
+          Assert (fixed_fields.find(compositional_field) != fixed_fields.end(),
+                  ExcMessage ("Boundary composition was requested for field " +
+                              Utilities::int_to_string(compositional_field) +
+                              " on boundary " +
+                              Utilities::int_to_string(boundary_indicator) +
+                              " but this field is not prescribed by the `ascii data` plugin. "));
+          field_id = std::distance(fixed_fields.begin(), fixed_fields.find(compositional_field));
+        }
+
       return Utilities::AsciiDataBoundary<dim>::get_data_component(boundary_indicator,
                                                                    position,
-                                                                   compositional_field);
+                                                                   field_id);
     }
 
     template <int dim>
@@ -109,11 +126,12 @@ namespace aspect
                                                "has to be `x', `composition1', `composition2', "
                                                "etc. in a 2d model and "
                                                "`x', `y', `composition1', `composition2', "
-                                               "etc., in a 3d model, according "
-                                               "to the number of compositional fields, which means that "
-                                               "there has to be a single column "
-                                               "for every composition in the model. "
-                                               "Note that the data in the input "
+                                               "etc., in a 3d model, with a column for each of "
+                                               "the compositional fields that are "
+                                               "prescribed by this plugin (on all boundaries). "
+                                               "This means that there has to be a single column "
+                                               "for every composition that is prescribed with `ascii data' "
+                                               "in the model. Note that the data in the input "
                                                "files need to be sorted in a specific order: "
                                                "the first coordinate needs to ascend first, "
                                                "followed by the second in order to "

source/boundary_composition/box.cc

@@ -40,7 +40,23 @@ namespace aspect
                           const unsigned int compositional_field) const
     {
       Assert (boundary_indicator<2*dim, ExcMessage ("The given boundary indicator needs to be less than 2*dimension.."));
-      return composition_values[boundary_indicator][compositional_field];
+
+      // In case not all fields are fixed on the boundary,
+      // figure out the right index of the given field.
+      unsigned int field_id = compositional_field;
+      if (this->get_boundary_composition_manager().boundaries_with_fixed_subset_of_fields_exist())
+        {
+          const std::set<unsigned int> fixed_fields = this->get_boundary_composition_manager().get_fixed_compositional_fields_for_plugin_on_boundary("box", boundary_indicator);
+          Assert (fixed_fields.find(compositional_field) != fixed_fields.end(),
+                  ExcMessage ("Boundary composition was requested for field " +
+                              Utilities::int_to_string(compositional_field) +
+                              " on boundary " +
+                              Utilities::int_to_string(boundary_indicator) +
+                              " but this field is not prescribed by the `box` plugin. "));
+          field_id = std::distance(fixed_fields.begin(), fixed_fields.find(compositional_field));
+        }
+
+      return composition_values[boundary_indicator][field_id];
     }
 
     template <int dim>
@@ -55,36 +71,42 @@ namespace aspect
                              Patterns::List(Patterns::Double ()),
                              "A comma separated list of composition boundary values "
                              "at the left boundary (at minimal $x$-value). This list must have as many "
-                             "entries as there are compositional fields. Units: none.");
+                             "entries as there are compositional fields prescribed by the plugin on the left boundary. "
+                             "Units: none.");
           prm.declare_entry ("Right composition", "",
                              Patterns::List(Patterns::Double ()),
                              "A comma separated list of composition boundary values "
                              "at the right boundary (at maximal $x$-value). This list must have as many "
-                             "entries as there are compositional fields. Units: none.");
+                             "entries as there are compositional fields prescribed by the plugin on the right boundary. "
+                             "Units: none.");
           prm.declare_entry ("Bottom composition", "",
                              Patterns::List(Patterns::Double ()),
                              "A comma separated list of composition boundary values "
                              "at the bottom boundary (at minimal $y$-value in 2d, or minimal "
                              "$z$-value in 3d). This list must have as many "
-                             "entries as there are compositional fields. Units: none.");
+                             "entries as there are compositional fields prescribed by the plugin on the bottom boundary. "
+                             "Units: none.");
           prm.declare_entry ("Top composition", "",
                              Patterns::List(Patterns::Double ()),
                              "A comma separated list of composition boundary values "
                              "at the top boundary (at maximal $y$-value in 2d, or maximal "
                              "$z$-value in 3d). This list must have as many "
-                             "entries as there are compositional fields. Units: none.");
+                             "entries as there are compositional fields prescribed by the plugin on the top boundary. "
+                             "Units: none.");
           if (dim==3)
             {
               prm.declare_entry ("Front composition", "",
                                  Patterns::List(Patterns::Double ()),
                                  "A comma separated list of composition boundary values "
                                  "at the front boundary (at minimum $y$-value). This list must have as many "
-                                 "entries as there are compositional fields. Units: none.");
+                                 "entries as there are compositional fields prescribed by the plugin on the front boundary. "
+                                 "Units: none.");
               prm.declare_entry ("Back composition", "",
                                  Patterns::List(Patterns::Double ()),
                                  "A comma separated list of composition boundary values "
                                  "at the back boundary (at maximum $y$-value). This list must have as many "
-                                 "entries as there are compositional fields. Units: none.");
+                                 "entries as there are compositional fields prescribed by the plugin on the back boundary. "
+                                 "Units: none.");
             }
         }
         prm.leave_subsection ();
@@ -143,24 +165,32 @@ namespace aspect
       // Verify that each of the lists for boundary values
       // has the requisite number of elements if it is in the set
       // of prescribed boundary indicators.
+      // Not all fields need to be fixed on a given boundary.
       for (unsigned int f=0; f<2*dim; ++f)
-        if (this->get_boundary_composition_manager().get_fixed_composition_boundary_indicators().count(f) != 0)
-          AssertThrow (composition_values[f].size() == this->n_compositional_fields(),
-                       ExcMessage (std::string("The specification of boundary composition values for the `box' model "
-                                               "requires as many values on each face of the box as there are compositional "
-                                               "fields. However, for face ")
-                                   +
-                                   Utilities::int_to_string(f)
-                                   +
-                                   ", the input file specifies "
-                                   +
-                                   Utilities::int_to_string(composition_values[f].size())
-                                   +
-                                   " values even though there are "
-                                   +
-                                   Utilities::int_to_string(this->n_compositional_fields())
-                                   +
-                                   " compositional fields."));
+        {
+          const std::set<types::boundary_id> fixed_boundary_indicators = this->get_boundary_composition_manager().get_fixed_compositional_fields_for_plugin_on_boundary("box",f);
+          if (fixed_boundary_indicators.count(f) != 0)
+            AssertThrow (composition_values[f].size() == fixed_boundary_indicators.size(),
+                         ExcMessage (std::string("The specification of boundary composition values for the `box' model "
+                                                 "requires as many values on each face of the box as there are "
+                                                 "compositional fields prescribed by the plugin on each face. However, for face ")
+                                     +
+                                     Utilities::int_to_string(f)
+                                     +
+                                     ", the input file specifies "
+                                     +
+                                     Utilities::int_to_string(composition_values[f].size())
+                                     +
+                                     " values even though there are "
+                                     +
+                                     Utilities::int_to_string(this->n_compositional_fields())
+                                     +
+                                     " compositional field(s) and "
+                                     +
+                                     Utilities::int_to_string(fixed_boundary_indicators.size())
+                                     +
+                                     " compositional field(s) prescribed by the plugin on this face."));
+        }
     }
 
   }