Allowing to define an array varible with component size one, refs ida…

…holab#19564

framework/include/actions/AddVariableAction.h

@@ -54,8 +54,10 @@ class AddVariableAction : public MooseObjectAction
   /**
    * determine the variable type given an FEType and number of components
    */
-  static std::string
-  determineType(const FEType & fe_type, unsigned int components, bool is_fv = false);
+  static std::string determineType(const FEType & fe_type,
+                                   unsigned int components,
+                                   bool is_fv = false,
+                                   bool is_array_variable = false);
 
 protected:
   /**

framework/src/actions/AddVariableAction.C

@@ -133,8 +133,10 @@ AddVariableAction::init()
 
   // Determine the MooseVariable type
   bool is_fv = _moose_object_pars.get<bool>("fv");
+  bool is_array_variable =
+      (_components > 1 || _moose_object_pars.get<bool>("array_variable")) ? true : false;
   if (_type == "MooseVariableBase")
-    _type = determineType(_fe_type, _components, is_fv);
+    _type = determineType(_fe_type, _components, is_fv, is_array_variable);
   if (is_fv)
     _problem->needFV();
 
@@ -223,12 +225,15 @@ AddVariableAction::createInitialConditionAction()
 }
 
 std::string
-AddVariableAction::determineType(const FEType & fe_type, unsigned int components, bool is_fv)
+AddVariableAction::determineType(const FEType & fe_type,
+                                 unsigned int components,
+                                 bool is_fv,
+                                 bool is_array_variable)
 {
   if (is_fv)
     return "MooseVariableFVReal";
 
-  if (components > 1)
+  if (components > 1 || is_array_variable)
   {
     if (fe_type.family == LAGRANGE_VEC || fe_type.family == NEDELEC_ONE ||
         fe_type.family == MONOMIAL_VEC)

framework/src/systems/SystemBase.C

@@ -823,6 +823,9 @@ SystemBase::addVariable(const std::string & var_type,
     // The number returned by libMesh is the _last_ variable number... we want to hold onto the
     // _first_
     var_num = system().add_variables(var_names, fe_type, &blocks) - (components - 1);
+
+    // Set as array variable
+    parameters.set<bool>("array_variable") = true;
   }
   else
     var_num = system().add_variable(name, fe_type, &blocks);

framework/src/variables/MooseVariableBase.C

@@ -62,6 +62,10 @@ MooseVariableBase::validParams()
                                      "Specifies a scaling factor to apply to this variable");
   params.addParam<bool>("eigen", false, "True to make this variable an eigen variable");
   params.addParam<bool>("fv", false, "True to make this variable a finite volume variable");
+  params.addParam<bool>(
+      "array_variable",
+      false,
+      "True to make this variable a array variable regardless of number of components");
   params.addParamNamesToGroup("scaling eigen", "Advanced");
 
   params.addParam<bool>("use_dual", false, "True to use dual basis for Lagrange multipliers");
@@ -107,8 +111,10 @@ MooseVariableBase::MooseVariableBase(const InputParameters & parameters)
     paramError("family", "finite volume (fv=true) variables must be have MONOMIAL family");
   if (getParam<bool>("fv") && _fe_type.order != 0)
     paramError("order", "finite volume (fv=true) variables currently support CONST order only");
-
-  if (_count > 1)
+  bool is_array_variable = getParam<bool>("array_variable");
+  if (!is_array_variable && _count > 1)
+    paramError("array_variable", "array_variable must be true if 'component' is greater than one");
+  if (is_array_variable)
   {
     auto name0 = _sys.system().variable(_var_num).name();
     std::size_t found = name0.find_last_of("_");
@@ -117,7 +123,10 @@ MooseVariableBase::MooseVariableBase(const InputParameters & parameters)
     _var_name = name0.substr(0, found);
   }
   else
+  {
+    mooseAssert(_count == 1, "component size of normal variable (_count) must be one");
     _var_name = _sys.system().variable(_var_num).name();
+  }
 }
 
 const std::vector<dof_id_type> &

test/tests/variables/array_variable/array_variable_size_one_test.i

@@ -0,0 +1,67 @@
+[Mesh]
+  [square]
+    type = GeneratedMeshGenerator
+    nx = 3
+    ny = 3
+    dim = 2
+  []
+[]
+
+[Variables]
+  [u]
+    order = THIRD
+    family = MONOMIAL
+    components = 1
+    array_variable = true
+  []
+[]
+
+[Kernels]
+  [diff]
+    type = ArrayDiffusion
+    variable = u
+    diffusion_coefficient = dc
+  []
+  [reaction]
+    type = ArrayReaction
+    variable = u
+    reaction_coefficient = rc
+  []
+  [source]
+    type = ArrayBodyForce
+    variable = u
+    function = '1'
+  []
+[]
+
+[BCs]
+  [all]
+    type = ArrayVacuumBC
+    boundary = 'left right top bottom'
+    variable = u
+  []
+[]
+
+[Materials]
+  [dc]
+    type = GenericConstantArray
+    prop_name = dc
+    prop_value = '1'
+  []
+  [rc]
+    type = GenericConstantArray
+    prop_name = rc
+    prop_value = '2'
+  []
+[]
+
+[Executioner]
+  type = Steady
+  solve_type = 'NEWTON'
+[]
+
+[Outputs]
+  [out]
+    type = Exodus
+  []
+[]

test/tests/variables/array_variable/tests

@@ -7,4 +7,12 @@
     issues = '#6881'
     design = 'ArrayMooseVariable.md'
   [../]
+  [./array_variable_size_one]
+    type = 'Exodiff'
+    input = 'array_variable_size_one_test.i'
+    exodiff = 'array_variable_size_one_test_out.e'
+    requirement = 'MOOSE shall be able to define an array varibale with component size one.'
+    issues = '#19564'
+    design = 'ArrayMooseVariable.md'
+  [../]
 []