Adding DifferencePostprocessor (closes idaholab#3268)

framework/include/postprocessors/DifferencePostprocessor.h

@@ -0,0 +1,33 @@
+#ifndef DIFFERENCEPOSTPROCESSOR_H
+#define DIFFERENCEPOSTPROCESSOR_H
+
+#include "GeneralPostprocessor.h"
+
+class DifferencePostprocessor;
+
+template<>
+InputParameters validParams<DifferencePostprocessor>();
+
+/**
+ * Computes the difference between two postprocessors
+ *
+ * result = value1 - value2
+ */
+class DifferencePostprocessor : public GeneralPostprocessor
+{
+public:
+  DifferencePostprocessor(const std::string & name, InputParameters parameters);
+  virtual ~DifferencePostprocessor();
+
+  virtual void initialize();
+  virtual void execute();
+  virtual PostprocessorValue getValue();
+  virtual void threadJoin(const UserObject & uo);
+
+protected:
+  const PostprocessorValue & _value1;
+  const PostprocessorValue & _value2;
+};
+
+
+#endif /* DIFFERENCEPOSTPROCESSOR_H */

framework/src/base/Moose.C

@@ -176,6 +176,7 @@
 #include "PointValue.h"
 #include "NodalExtremeValue.h"
 #include "ElementExtremeValue.h"
+#include "DifferencePostprocessor.h"
 
 // vector PPS
 #include "ConstantVectorPostprocessor.h"
@@ -516,6 +517,7 @@ registerObjects(Factory & factory)
   registerPostprocessor(PointValue);
   registerPostprocessor(NodalExtremeValue);
   registerPostprocessor(ElementExtremeValue);
+  registerPostprocessor(DifferencePostprocessor);
 
   // vector PPS
   registerVectorPostprocessor(ConstantVectorPostprocessor);

framework/src/postprocessors/DifferencePostprocessor.C

@@ -0,0 +1,44 @@
+#include "DifferencePostprocessor.h"
+
+template<>
+InputParameters validParams<DifferencePostprocessor>()
+{
+  InputParameters params = validParams<GeneralPostprocessor>();
+  params.addRequiredParam<PostprocessorName>("value1", "First value");
+  params.addRequiredParam<PostprocessorName>("value2", "Second value");
+
+  return params;
+}
+
+DifferencePostprocessor::DifferencePostprocessor(const std::string & name, InputParameters parameters) :
+    GeneralPostprocessor(name, parameters),
+    _value1(getPostprocessorValue("value1")),
+    _value2(getPostprocessorValue("value2"))
+{
+}
+
+DifferencePostprocessor::~DifferencePostprocessor()
+{
+}
+
+void
+DifferencePostprocessor::initialize()
+{
+}
+
+void
+DifferencePostprocessor::execute()
+{
+}
+
+PostprocessorValue
+DifferencePostprocessor::getValue()
+{
+  return _value1 - _value2;
+}
+
+void
+DifferencePostprocessor::threadJoin(const UserObject & /*uo*/)
+{
+  // nothing to do here, general PPS do not run threaded
+}

test/tests/postprocessors/difference_pps/difference_pps.i

@@ -0,0 +1,90 @@
+[Mesh]
+  type = GeneratedMesh
+  dim = 2
+  xmin = 0
+  xmax = 1
+  ymin = 0
+  ymax = 1
+  nx = 2
+  ny = 2
+[]
+
+[AuxVariables]
+  [./v]
+  [../]
+[]
+
+[Variables]
+  [./u]
+  [../]
+[]
+
+[ICs]
+  [./u_ic]
+    type = ConstantIC
+    variable = u
+    value = 2
+  [../]
+[]
+
+[AuxKernels]
+  [./one]
+    type = ConstantAux
+    variable = v
+    value = 1
+  [../]
+[]
+
+[Kernels]
+  [./diff]
+    type = Diffusion
+    variable = u
+  [../]
+[]
+
+[BCs]
+  [./left]
+    type = DirichletBC
+    variable = u
+    boundary = left
+    value = 0
+  [../]
+  [./right]
+    type = DirichletBC
+    variable = u
+    boundary = right
+    value = 1
+  [../]
+[]
+
+[Postprocessors]
+  [./u_avg]
+    type = ElementAverageValue
+    variable = u
+  [../]
+
+  [./v_avg]
+    type = ElementAverageValue
+    variable = v
+  [../]
+
+  [./diff]
+    type = DifferencePostprocessor
+    value1 = v_avg
+    value2 = u_avg
+  [../]
+[]
+
+[Executioner]
+  type = Steady
+[]
+
+[Outputs]
+  output_initial = true
+  exodus = true
+  [./console]
+    type = Console
+    perf_log = true
+    linear_residuals = true
+  [../]
+[]

test/tests/postprocessors/difference_pps/tests

@@ -0,0 +1,7 @@
+[Tests]
+  [./test]
+    type = 'Exodiff'
+    input = 'difference_pps.i'
+    exodiff = 'difference_pps_out.e'
+  [../]
+[]