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

* Clean up the use of ndt for collisions

* Update BackgroundStopping to match changes

1 files changed, 5 insertions, 2 deletions

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);
+        }
     }
 
 }