Add add increment application with variable change capability

src/CMakeLists.txt

@@ -5,5 +5,6 @@ if ( oops_FOUND )
   add_subdirectory( ioda-stats )
   add_subdirectory( ioda-summary )
   add_subdirectory( ioda-dump )
-  add_subdirectory(gsi_varbc)
+  add_subdirectory( gsi_varbc )
+  add_subdirectory( add_increment )
 endif()

src/add_increment/CMakeLists.txt

@@ -0,0 +1,11 @@
+# AddIncrement
+ecbuild_add_executable( TARGET fv3jedi_add_increment.x
+                        SOURCES fv3jedi_add_increment.cc add_increment.h)
+target_compile_features( fv3jedi_add_increment.x PUBLIC cxx_std_17)
+target_link_libraries( fv3jedi_add_increment.x PUBLIC NetCDF::NetCDF_CXX oops fv3jedi)
+
+# Ensemble AddIncrement
+ecbuild_add_executable( TARGET fv3jedi_ensemble_add_increment.x
+                        SOURCES fv3jedi_ensemble_add_increment.cc add_increment.h)
+target_compile_features( fv3jedi_ensemble_add_increment.x PUBLIC cxx_std_17)
+target_link_libraries( fv3jedi_ensemble_add_increment.x PUBLIC NetCDF::NetCDF_CXX oops fv3jedi)

src/add_increment/add_increment.h

@@ -0,0 +1,119 @@
+/*
+ * (C) Copyright 2026 NOAA
+ *
+ * This software is licensed under the terms of the Apache Licence Version 2.0
+ * which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+ */
+
+#ifndef OOPS_RUNS_ADDINCREMENT_H_
+#define OOPS_RUNS_ADDINCREMENT_H_
+
+#include <string>
+#include <vector>
+
+#include "oops/base/Geometry.h"
+#include "oops/base/Increment.h"
+#include "oops/base/State.h"
+#include "oops/base/Variables.h"
+#include "oops/interface/VariableChange.h"
+#include "oops/mpi/mpi.h"
+#include "oops/runs/Application.h"
+#include "oops/util/DateTime.h"
+#include "oops/util/Duration.h"
+#include "oops/util/Logger.h"
+
+namespace dautils {
+
+/// Application that adds an increment to a state and writes the sum to a file.
+///
+/// The increment may optionally be multiplied by a scaling factor and have a different resolution
+/// than the state.
+template <typename MODEL> class AddIncrement : public oops::Application {
+  typedef oops::Geometry<MODEL>       Geometry_;
+  typedef oops::State<MODEL>          State_;
+  typedef oops::Increment<MODEL>      Increment_;
+  typedef oops::VariableChange<MODEL> VariableChange_;
+
+ public:
+// -----------------------------------------------------------------------------
+  explicit AddIncrement(const eckit::mpi::Comm & comm = oops::mpi::world()) : Application(comm) {}
+// -----------------------------------------------------------------------------
+  virtual ~AddIncrement() {}
+// -----------------------------------------------------------------------------
+  int execute(const eckit::Configuration & fullConfig) const override {
+//  Setup resolution
+    const Geometry_ stateResol(eckit::LocalConfiguration(fullConfig, "state geometry"),
+                               this->getComm());
+
+    const Geometry_ incResol(eckit::LocalConfiguration(fullConfig, "increment geometry"),
+                             this->getComm());
+
+//  Read state
+    State_ xx(stateResol, eckit::LocalConfiguration(fullConfig, "state"));
+    oops::Log::test() << "State: " << xx << std::endl;
+
+//  Read increment
+    const eckit::LocalConfiguration incParams(fullConfig, "increment");
+    oops::Variables addedVars(incParams, "added variables");
+    Increment_ dx(incResol, addedVars, xx.validTime());
+    dx.read(incParams);
+    oops::Log::test() << "Increment: " << dx << std::endl;
+
+//  Scale increment
+    if (incParams.has("scaling factor")) {
+      dx *= incParams.getDouble("scaling factor");
+      oops::Log::test() << "Scaled the increment: " << dx << std::endl;
+    }
+
+//  Assertions on state versus increment
+    ASSERT(xx.validTime() == dx.validTime());
+
+//  Add increment to state
+    xx += dx;
+
+//  Optional variable change to recomputed chosen state variables in final state
+//  This is useful if, for example, the state has both delp and ps but the increment only has 
+//  delp. Simple increment addition of just delp to the state would result in an incorrect ps 
+//  value since ps is a function of delp. ps would need to be recalculated after the increment addition.
+    if ( fullConfig.has("variable change") ) {
+      // Setup variable change
+      const eckit::LocalConfiguration varChangeConfig(fullConfig, "variable change");
+      std::unique_ptr<VariableChange_> vc;
+      vc.reset(new VariableChange_(varChangeConfig, stateResol));
+
+      // Get additional variables to be derived by variable change
+      oops::Variables varsChanged(varChangeConfig, "recalculated variables");
+
+      // Save state variables with and without variable change variables
+      oops::Variables stateVarsReduced = xx.variables();
+      oops::Variables stateVarsExpanded = xx.variables();
+      stateVarsReduced -= varsChanged;
+      stateVarsExpanded += varsChanged;
+
+      // Change state to reduced set of variables
+      // This is necessary since a variable needs to be missing from the state in order
+      // for it to be computed by the final variable change.
+      vc->changeVar(xx, stateVarsReduced);
+
+      // Change variables to expanded set of variables
+      // This step actually computes the variables we want
+      vc->changeVar(xx, stateVarsExpanded);
+    }
+
+//  Write state
+    xx.write(eckit::LocalConfiguration(fullConfig, "output"));
+
+    oops::Log::test() << "State plus increment: " << xx << std::endl;
+
+    return 0;
+  }
+// -----------------------------------------------------------------------------
+ private:
+  std::string appname() const override {
+    return "dautils::AddIncrement<" + MODEL::name() + ">";
+  }
+// -----------------------------------------------------------------------------
+};
+
+}  // namespace oops
+#endif  // OOPS_RUNS_ADDINCREMENT_H_

src/add_increment/fv3jedi_add_increment.cc

@@ -0,0 +1,11 @@
+#include "add_increment.h"
+
+#include "fv3jedi/Utilities/Traits.h"
+
+#include "oops/runs/Run.h"
+
+int main(int argc,  char ** argv) {
+  oops::Run run(argc, argv);
+  dautils::AddIncrement<fv3jedi::Traits> addIncrement;
+  return run.execute(addIncrement);
+}

src/add_increment/fv3jedi_ensemble_add_increment.cc

@@ -0,0 +1,12 @@
+#include "add_increment.h"
+
+#include "fv3jedi/Utilities/Traits.h"
+
+#include "oops/runs/EnsembleApplication.h"
+#include "oops/runs/Run.h"
+
+int main(int argc,  char ** argv) {
+  oops::Run run(argc, argv);
+  oops::EnsembleApplication<dautils::AddIncrement<fv3jedi::Traits>> addIncrement;
+  return run.execute(addIncrement);
+}