Clean up the use of ndt for collisions (#2944)

* Clean up the use of ndt for collisions

* Update BackgroundStopping to match changes

8 files changed, 24 insertions, 28 deletions

diff --git a/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.H b/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.H
index ff447c407..e4ad27d04 100644
--- a/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.H
+++ b/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.H
@@ -32,10 +32,11 @@ public:
     /** Perform the collisions
      *
      * @param cur_time Current time
+     * @param dt Time step size
      * @param mypc Container of species involved
      *
      */
-    void doCollisions (amrex::Real cur_time, MultiParticleContainer* mypc) override;
+    void doCollisions (amrex::Real cur_time, amrex::Real dt, MultiParticleContainer* mypc) override;
 
     /** Perform particle conserving MCC collisions within a tile
      *
diff --git a/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.cpp b/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.cpp
index 615fb9418..a7cc00be5 100644
--- a/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.cpp
+++ b/Source/Particles/Collision/BackgroundMCC/BackgroundMCCCollision.cpp
@@ -181,14 +181,11 @@ BackgroundMCCCollision::get_nu_max(amrex::Vector<MCCProcess> const& mcc_processe
 }
 
 void
-BackgroundMCCCollision::doCollisions (amrex::Real cur_time, MultiParticleContainer* mypc)
+BackgroundMCCCollision::doCollisions (amrex::Real cur_time, amrex::Real dt, MultiParticleContainer* mypc)
 {
     WARPX_PROFILE("BackgroundMCCCollision::doCollisions()");
     using namespace amrex::literals;
 
-    const amrex::Real dt = WarpX::GetInstance().getdt(0);
-    if ( int(std::floor(cur_time/dt)) % m_ndt != 0 ) return;
-
     auto& species1 = mypc->GetParticleContainerFromName(m_species_names[0]);
     // this is a very ugly hack to have species2 be a reference and be
     // defined in the scope of doCollisions
@@ -205,7 +202,7 @@ BackgroundMCCCollision::doCollisions (amrex::Real cur_time, MultiParticleContain
         m_nu_max = get_nu_max(m_scattering_processes);
 
         // calculate total collision probability
-        auto coll_n = m_nu_max * m_ndt * dt;
+        auto coll_n = m_nu_max * dt;
         m_total_collision_prob = 1.0_rt - std::exp(-coll_n);
 
         // dt has to be small enough that a linear expansion of the collision
@@ -220,7 +217,7 @@ BackgroundMCCCollision::doCollisions (amrex::Real cur_time, MultiParticleContain
             m_nu_max_ioniz = get_nu_max(m_ionization_processes);
 
             // calculate total ionization probability
-            auto coll_n_ioniz = m_nu_max_ioniz * m_ndt * dt;
+            auto coll_n_ioniz = m_nu_max_ioniz * dt;
             m_total_collision_prob_ioniz = 1.0_rt - std::exp(-coll_n_ioniz);
 
             WARPX_ALWAYS_ASSERT_WITH_MESSAGE(coll_n_ioniz < 0.1_rt,
diff --git a/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.H b/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.H
index 698943918..56538102f 100644
--- a/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.H
+++ b/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.H
@@ -31,10 +31,11 @@ public:
     /** Perform the stopping calculation
      *
      * @param cur_time Current time
+     * @param dt Time step size
      * @param mypc Container of species involved
      *
      */
-    void doCollisions (amrex::Real cur_time, MultiParticleContainer* mypc) override;
+    void doCollisions (amrex::Real cur_time, amrex::Real dt, MultiParticleContainer* mypc) override;
 
     /** Perform the stopping calculation within a tile for stopping on electrons
      *
diff --git a/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.cpp b/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.cpp
index dd51a3d0d..a970c490f 100644
--- a/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.cpp
+++ b/Source/Particles/Collision/BackgroundStopping/BackgroundStopping.cpp
@@ -75,16 +75,11 @@ BackgroundStopping::BackgroundStopping (std::string const collision_name)
 }
 
 void
-BackgroundStopping::doCollisions (amrex::Real cur_time, MultiParticleContainer* mypc)
+BackgroundStopping::doCollisions (amrex::Real cur_time, amrex::Real dt, MultiParticleContainer* mypc)
 {
     WARPX_PROFILE("BackgroundStopping::doCollisions()");
     using namespace amrex::literals;
 
-    // Note that the lowest level time step is used for all levels since the
-    // collision operation will be done only once per step at the lowest level.
-    const amrex::Real dt = WarpX::GetInstance().getdt(0) * m_ndt;
-    if (int(std::floor(cur_time/dt)) % m_ndt != 0) return;
-
     auto& species = mypc->GetParticleContainerFromName(m_species_names[0]);
     amrex::Real species_mass = species.getMass();
     amrex::Real species_charge = species.getCharge();
diff --git a/Source/Particles/Collision/BinaryCollision/BinaryCollision.H b/Source/Particles/Collision/BinaryCollision/BinaryCollision.H
index 217547cf9..fd33c0ff4 100644
--- a/Source/Particles/Collision/BinaryCollision/BinaryCollision.H
+++ b/Source/Particles/Collision/BinaryCollision/BinaryCollision.H
@@ -107,13 +107,12 @@ public:
     /** Perform the collisions
      *
      * @param cur_time Current time
+     * @param dt Time step size
      * @param mypc Container of species involved
      *
      */
-    void doCollisions (amrex::Real cur_time, MultiParticleContainer* mypc) override
+    void doCollisions (amrex::Real /*cur_time*/, amrex::Real dt, MultiParticleContainer* mypc) override
     {
-        const amrex::Real dt = WarpX::GetInstance().getdt(0);
-        if ( int(std::floor(cur_time/dt)) % m_ndt != 0 ) return;
 
         auto& species1 = mypc->GetParticleContainerFromName(m_species_names[0]);
         auto& species2 = mypc->GetParticleContainerFromName(m_species_names[1]);
@@ -178,7 +177,7 @@ public:
                 }
                 amrex::Real wt = amrex::second();
 
-                doCollisionsWithinTile( lev, mfi, species1, species2, product_species_vector,
+                doCollisionsWithinTile( dt, lev, mfi, species1, species2, product_species_vector,
                                          copy_species1_data, copy_species2_data);
 
                 if (cost && WarpX::load_balance_costs_update_algo == LoadBalanceCostsUpdateAlgo::Timers)
@@ -203,7 +202,7 @@ public:
      *
      */
     void doCollisionsWithinTile (
-        int const lev, amrex::MFIter const& mfi,
+        amrex::Real dt, int const lev, amrex::MFIter const& mfi,
         WarpXParticleContainer& species_1,
         WarpXParticleContainer& species_2,
         amrex::Vector<WarpXParticleContainer*> product_species_vector,
@@ -212,7 +211,6 @@ public:
         using namespace ParticleUtils;
         using namespace amrex::literals;
 
-        int const ndt = m_ndt;
         CollisionFunctorType binary_collision_functor = m_binary_collision_functor;
         const bool have_product_species = m_have_product_species;
 
@@ -255,7 +253,6 @@ public:
             ParticleType * AMREX_RESTRICT
                                  particle_ptr_1 = ptile_1.GetArrayOfStructs()().data();
 
-            const amrex::Real dt = WarpX::GetInstance().getdt(lev);
             amrex::Geometry const& geom = WarpX::GetInstance().Geom(lev);
 #if defined WARPX_DIM_1D_Z
             auto dV = geom.CellSize(0);
@@ -350,7 +347,7 @@ public:
                         cell_half_1, cell_stop_1,
                         indices_1, indices_1,
                         soa_1, soa_1, get_position_1, get_position_1,
-                        q1, q1, m1, m1, dt*ndt, dV,
+                        q1, q1, m1, m1, dt, dV,
                         cell_start_pair, p_mask, p_pair_indices_1, p_pair_indices_2,
                         p_pair_reaction_weight, engine );
                 }
@@ -406,7 +403,6 @@ public:
             ParticleType * AMREX_RESTRICT
                                  particle_ptr_2 = ptile_2.GetArrayOfStructs()().data();
 
-            const amrex::Real dt = WarpX::GetInstance().getdt(lev);
             amrex::Geometry const& geom = WarpX::GetInstance().Geom(lev);
 #if defined WARPX_DIM_1D_Z
             auto dV = geom.CellSize(0);
@@ -511,7 +507,7 @@ public:
                         cell_start_1, cell_stop_1, cell_start_2, cell_stop_2,
                         indices_1, indices_2,
                         soa_1, soa_2, get_position_1, get_position_2,
-                        q1, q2, m1, m2, dt*ndt, dV,
+                        q1, q2, m1, m2, dt, dV,
                         cell_start_pair, p_mask, p_pair_indices_1, p_pair_indices_2,
                         p_pair_reaction_weight, engine );
                 }
diff --git a/Source/Particles/Collision/CollisionBase.H b/Source/Particles/Collision/CollisionBase.H
index 3d79857e0..517f5e414 100644
--- a/Source/Particles/Collision/CollisionBase.H
+++ b/Source/Particles/Collision/CollisionBase.H
@@ -20,13 +20,16 @@ public:
 
     CollisionBase (std::string collision_name);
 
-    virtual void doCollisions (amrex::Real /*cur_time*/, MultiParticleContainer* /*mypc*/ ){}
+    virtual void doCollisions (amrex::Real /*cur_time*/, amrex::Real /*dt*/, MultiParticleContainer* /*mypc*/ ){}
 
     CollisionBase(CollisionBase const &) = delete;
     CollisionBase(CollisionBase &&) = delete;
     CollisionBase & operator=(CollisionBase const &) = delete;
 
     virtual ~CollisionBase() = default;
+
+    int get_ndt() {return m_ndt;}
+
 protected:
 
     amrex::Vector<std::string> m_species_names;
diff --git a/Source/Particles/Collision/CollisionHandler.H b/Source/Particles/Collision/CollisionHandler.H
index 41a7a0696..7adc15dec 100644
--- a/Source/Particles/Collision/CollisionHandler.H
+++ b/Source/Particles/Collision/CollisionHandler.H
@@ -26,7 +26,7 @@ public:
     CollisionHandler (MultiParticleContainer const * const mypc);
 
     /* Perform all of the collisions */
-    void doCollisions (amrex::Real cur_time, MultiParticleContainer* mypc);
+    void doCollisions (amrex::Real cur_time, amrex::Real dt, MultiParticleContainer* mypc);
 
 private:
 
diff --git a/Source/Particles/Collision/CollisionHandler.cpp b/Source/Particles/Collision/CollisionHandler.cpp
index 0c5304823..cc8d8eb4a 100644
--- a/Source/Particles/Collision/CollisionHandler.cpp
+++ b/Source/Particles/Collision/CollisionHandler.cpp
@@ -71,11 +71,14 @@ CollisionHandler::CollisionHandler(MultiParticleContainer const * const mypc)
  * @param mypc MultiParticleContainer calling this method
  *
  */
-void CollisionHandler::doCollisions ( amrex::Real cur_time, MultiParticleContainer* mypc)
+void CollisionHandler::doCollisions ( amrex::Real cur_time, amrex::Real dt, MultiParticleContainer* mypc)
 {
 
     for (auto& collision : allcollisions) {
-        collision->doCollisions(cur_time, mypc);
+        int const ndt = collision->get_ndt();
+        if ( int(std::floor(cur_time/dt)) % ndt == 0 ) {
+            collision->doCollisions(cur_time, dt*ndt, mypc);
+        }
     }
 
 }