Options periodicY function

src/field/field_factory.cxx

@@ -1,7 +1,7 @@
 /**************************************************************************
- * Copyright 2010 B.D.Dudson, S.Farley, M.V.Umansky, X.Q.Xu
+ * Copyright 2010-2025 BOUT++ contributors
  *
- * Contact: Ben Dudson, bd512@york.ac.uk
+ * Contact: Ben Dudson, dudson2@llnl.gov
  *
  * This file is part of BOUT++.
  *
@@ -176,6 +176,9 @@ FieldFactory::FieldFactory(Mesh* localmesh, Options* opt)
 
   // Where switch function
   addGenerator("where", std::make_shared<FieldWhere>(nullptr, nullptr, nullptr));
+
+  // Periodic in the Y direction?
+  addGenerator("periodicY", std::make_shared<FieldPeriodicY>(nullptr));
 }
 
 Field2D FieldFactory::create2D(const std::string& value, const Options* opt,

src/field/fieldgenerators.hxx

@@ -1,4 +1,4 @@
-/*!
+/*!A
  * \file fieldgenerators.hxx
  *
  * These classes are used by FieldFactory
@@ -352,4 +352,34 @@ private:
   FieldGeneratorPtr test, gt0, lt0;
 };
 
+/// Function that evaluates to 1 when Y is periodic (i.e. in the core), 0 otherwise
+class FieldPeriodicY : public FieldGenerator {
+public:
+  FieldPeriodicY(Mesh* mesh) : mesh(mesh) {
+    // Note: Assumes symmetricGlobalX
+    local_inner_boundary =
+        0.5 * (mesh->GlobalX(mesh->xstart - 1) + mesh->GlobalX(mesh->xstart));
+    local_outer_boundary =
+        0.5 * (mesh->GlobalX(mesh->xend + 1) + mesh->GlobalX(mesh->xend));
+  }
+  FieldGeneratorPtr clone(const std::list<FieldGeneratorPtr> UNUSED(args)) override {
+    return std::make_shared<FieldPeriodicY>(ctx.getMesh());
+  }
+  BoutReal generate(const bout::generator::Context& ctx) override {
+    int local_index = mesh->xstart
+                      + int(((ctx.x() - local_inner_boundary)
+                             / (local_outer_boundary - local_inner_boundary))
+                            * (mesh->xend - mesh->xstart + 1));
+    if (mesh->periodicY(local_index)) {
+      return 1.0;
+    }
+    return 0.0;
+  }
+
+private:
+  Mesh* mesh;
+  BoutReal local_inner_boundary;
+  BoutReal local_outer_boundary;
+};
+
 #endif // BOUT_FIELDGENERATORS_H