Add a method to extract some states of the particles --...

Add a method to extract some states of the particles -- extractParticlesState(0,3) should return the positions

bfps/cpp/particles/abstract_particles_system.hpp

@@ -35,6 +35,8 @@ public:
 
     virtual const real_number* getParticlesState() const = 0;
 
+    virtual std::unique_ptr<real_number[]> extractParticlesState(const int firstState, const int lastState) const = 0;
+
     virtual const std::unique_ptr<real_number[]>* getParticlesRhs() const = 0;
 
     virtual const partsize_t* getParticlesIndexes() const = 0;

bfps/cpp/particles/particles_system.hpp

@@ -17,6 +17,8 @@
 template <class partsize_t, class real_number, class field_rnumber, class field_class, class interpolator_class, int interp_neighbours,
           int size_particle_positions, int size_particle_rhs, class p2p_computer_class, class particles_inner_computer_class>
 class particles_system : public abstract_particles_system<partsize_t, real_number> {
+    static_assert(size_particle_positions >= 3, "There should be at least the positions X,Y,Z in the state");
+
     MPI_Comm mpi_com;
 
     const std::pair<int,int> current_partition_interval;
@@ -272,6 +274,20 @@ public:
         return my_particles_positions.get();
     }
 
+    std::unique_ptr<real_number[]> extractParticlesState(const int firstState, const int lastState) const final {
+        const int nbStates = std::max(0,(std::min(lastState,size_particle_positions)-firstState));
+
+        std::unique_ptr<real_number[]> stateExtract(new real_number[my_nb_particles*nbStates]);
+
+        for(partsize_t idx_part = 0 ; idx_part < my_nb_particles ; ++idx_part){
+            for(int idxState = 0 ; idxState < nbStates ; ++idxState){
+                stateExtract[idx_part*nbStates + idxState] = my_particles_positions[idx_part*size_particle_positions + idxState+firstState];
+            }
+        }
+
+        return stateExtract;
+    }
+
     const std::unique_ptr<real_number[]>* getParticlesRhs() const final {
         return my_particles_rhs.data();
     }