diff --git a/Homework4/src/compute_gravity.hh b/Homework4/src/compute_gravity.hh
index 2c308df..77071bd 100644
--- a/Homework4/src/compute_gravity.hh
+++ b/Homework4/src/compute_gravity.hh
@@ -1,28 +1,27 @@
 #ifndef __COMPUTE_GRAVITY__HH__
 #define __COMPUTE_GRAVITY__HH__
 
 /* -------------------------------------------------------------------------- */
 #include "compute_interaction.hh"
 
 //! Compute Newton gravity interaction
 class ComputeGravity : public ComputeInteraction {
 
   // Virtual implementation
 public:
   //! Newton gravity implementation
   void compute(System& system) override;
 
   // Accessors
 public:
   //! set the gravitational constant
   void setG(Real G);
 
   // Members
 private:
   //! newton constant
-  //Real G = 1.;
-  Real G = 6.67384e-11*5.97219e24*std::pow(60.0*60.0*24.0,2)/std::pow(149597870.7*1000.0,3);
+  Real G = 1.;
 };
 
 /* -------------------------------------------------------------------------- */
 #endif  //__COMPUTE_GRAVITY__HH__
diff --git a/Homework4/src/pypart.cc b/Homework4/src/pypart.cc
index c972770..678227f 100644
--- a/Homework4/src/pypart.cc
+++ b/Homework4/src/pypart.cc
@@ -1,163 +1,144 @@
 #include <functional>
 #include <iostream>
 #include <memory>
 #include <pybind11/pybind11.h>
 
 #include "my_types.hh"
 #include "fft.hh"
 #include "system_evolution.hh"
 #include "particles_factory_interface.hh"
 #include "material_points_factory.hh"
 #include "planets_factory.hh"
 #include "ping_pong_balls_factory.hh"
 #include "csv_writer.hh"
 #include "compute.hh"
 #include "compute_temperature.hh"
 #include "compute_interaction.hh"
 #include "compute_gravity.hh"
 #include "compute_verlet_integration.hh"
 
 namespace py = pybind11;
 
 PYBIND11_MODULE(pypart, m) {
     m.doc() = "Python binding for the particles code.";
-    
+
     // ========== Class System ==================================================================
     py::class_<System>(m, "System");
-    
-    
-    
+
+
+
     // ========== Class SystemEvolution =========================================================
     py::class_<SystemEvolution, std::unique_ptr<SystemEvolution>>(m, "SystemEvolution",
                                                                   py::dynamic_attr())
         .def(py::init([](std::unique_ptr<System>()){return std::unique_ptr<SystemEvolution>();}),
              py::return_value_policy::move)
         .def("evolve",      &SystemEvolution::evolve)
         .def("addCompute",  &SystemEvolution::addCompute)
         .def("getSystem",   &SystemEvolution::getSystem, py::return_value_policy::reference)
         .def("setNSteps",   &SystemEvolution::setNSteps)
         .def("setDumpFreq", &SystemEvolution::setDumpFreq);
-    
-    
-    
+
+
+
     // ========== Class ParticlesFactoryInterface ===============================================
     py::class_<ParticlesFactoryInterface>(m, "ParticlesFactoryInterface",
                                           py::dynamic_attr())
-        .def_static("getInstance", &ParticlesFactoryInterface::getInstance,
+        .def("getInstance", &ParticlesFactoryInterface::getInstance,
                     py::return_value_policy::reference)
-        .def("getSystemEvolution", &ParticlesFactoryInterface::getSystemEvolution,
-             py::return_value_policy::reference)
         .def_property_readonly("system_evolution",
-                               &ParticlesFactoryInterface::getSystemEvolution);
-    
-    
-    
+                    &ParticlesFactoryInterface::getSystemEvolution);
+
+
+
     // ========== Class MaterialPointsFactory ===================================================
     py::class_<MaterialPointsFactory,ParticlesFactoryInterface>(m, "MaterialPointsFactory",
                                                                 py::dynamic_attr())
-        .def_static("getInstance", &MaterialPointsFactory::getInstance,
-                    py::return_value_policy::reference)
-        .def("createSimulation",
-             (SystemEvolution& (MaterialPointsFactory::*)(const std::string &,Real))
-             &MaterialPointsFactory::createSimulation,
-             py::return_value_policy::reference)
-        .def("createSimulation",
-             (SystemEvolution& (MaterialPointsFactory::*)(const std::string &,Real,py::object))
-             &MaterialPointsFactory::createSimulation,
-             py::return_value_policy::reference);
-    
-    
-    
+        .def("createSimulation", py::overload_cast<const std::string&, Real, py::function>
+                    (&ParticlesFactoryInterface::createSimulation<py::function>), py::return_value_policy::reference)
+        .def("getInstance", &MaterialPointsFactory::getInstance,
+                    py::return_value_policy::reference);
+
+
+
     // ========== Class PlanetsFactory ==========================================================
     py::class_<PlanetsFactory, ParticlesFactoryInterface>(m, "PlanetsFactory",
                                                           py::dynamic_attr())
-        .def_static("getInstance", &PlanetsFactory::getInstance,
-                    py::return_value_policy::reference)
-        .def("createSimulation",
-             (SystemEvolution& (PlanetsFactory::*)(const std::string &,Real))
-             &PlanetsFactory::createSimulation,
-             py::return_value_policy::reference)
-        .def("createSimulation",
-             (SystemEvolution& (PlanetsFactory::*)(const std::string &,Real,py::object))
-             &PlanetsFactory::createSimulation,
-             py::return_value_policy::reference);
-    
-    
-    
+        .def("createSimulation", py::overload_cast<const std::string&, Real, py::function>
+                    (&ParticlesFactoryInterface::createSimulation<py::function>), py::return_value_policy::reference)
+        .def("getInstance", &PlanetsFactory::getInstance,
+                    py::return_value_policy::reference);
+
+
     // ========== Class PingPongBallsFactory ====================================================
     py::class_<PingPongBallsFactory, ParticlesFactoryInterface>(m, "PingPongBallsFactory",
                                                                 py::dynamic_attr())
-    .def_static("getInstance", &PingPongBallsFactory::getInstance,
-                py::return_value_policy::reference)
-    .def("createSimulation", (SystemEvolution& (PingPongBallsFactory::*)(const std::string &,
-                                                                         Real))
-         &PingPongBallsFactory::createSimulation,
-         py::return_value_policy::reference)
-    .def("createSimulation",(SystemEvolution& (PingPongBallsFactory::*)(const std::string &,
-                                                                        Real, py::object))
-         &PingPongBallsFactory::createSimulation,
-         py::return_value_policy::reference);
-    
-    
-    
+    .def("createSimulation", py::overload_cast<const std::string&, Real, py::function>
+                (&ParticlesFactoryInterface::createSimulation<py::function>), py::return_value_policy::reference)
+    .def("getInstance", &PingPongBallsFactory::getInstance,
+                py::return_value_policy::reference);
+
+
+
+
+
     // ========== Class Compute =================================================================
     py::class_<Compute, std::shared_ptr<Compute>>(m, "Compute");
 
     class Pycompute : public Compute{
     public:
         using Compute::Compute;
         void compute(System &system) override{
             PYBIND11_OVERLOAD_PURE(void, Compute, compute, system);
         }
     };
-    
-    
-    
+
+
+
     // ========== Class ComputeTemperature ======================================================
     py::class_<ComputeTemperature, Compute,
                     std::shared_ptr<ComputeTemperature>>(m, "ComputeTemperature",
                                                          py::dynamic_attr())
         .def(py::init<>())
         .def("compute", &ComputeTemperature::compute,
              py::return_value_policy::reference)
         .def_property_readonly("conductivity", &ComputeTemperature::getConductivity)
         .def_property_readonly("capacity",     &ComputeTemperature::getCapacity)
         .def_property_readonly("density",      &ComputeTemperature::getDensity)
         .def_property_readonly("L",            &ComputeTemperature::getL)
         .def_property_readonly("deltat",       &ComputeTemperature::getDeltat);
-    
-    
-    
+
+
+
     // ========== Class ComputeInteraction ======================================================
     py::class_<ComputeInteraction, Compute,
                     std::shared_ptr<ComputeInteraction>>(m, "ComputeInteraction",
                                                          py::dynamic_attr());
-    
-    
-    
+
+
+
     // ========== Class ComputeGravity ==========================================================
     py::class_<ComputeGravity, ComputeInteraction,
                 std::shared_ptr<ComputeGravity>>(m, "ComputeGravity",
                                                      py::dynamic_attr())
     .def(py::init<>())
     .def("compute", &ComputeGravity::compute,
          py::return_value_policy::reference)
     .def("setG",   &ComputeGravity::setG);
-    
-    
+
+
     // ========== Class ComputeVerletIntegration ================================================
     py::class_<ComputeVerletIntegration, Compute,
                 std::shared_ptr<ComputeVerletIntegration>>(m, "ComputeVerletIntegration",
                                                            py::dynamic_attr())
     .def(py::init<Real>())
     .def("compute", &ComputeVerletIntegration::compute,
          py::return_value_policy::reference)
     .def("addInteraction", &ComputeVerletIntegration::addInteraction)
     .def("setDeltaT",      &ComputeVerletIntegration::setDeltaT);
-    
-    
+
+
     // ========== Class CsvWriter ===============================================================
     py::class_<CsvWriter,Compute,std::shared_ptr<CsvWriter>>(m,"CsvWriter")
         .def(py::init<const std::string &>())
         .def("write", &CsvWriter::write);
 }