Functionality to save particle positions from the previous step (#2206)

* added functionality to save particle positions from the previous step
* copied WarpX variable to local variable to fix issue with GPU and DPC++ compilation
* switched to using a species attribute to toggle whether previous positions are saved so it can be turned on for only a subset of species if desired
* changed variable name to be more verbose
* added CI test of saving the previous particle positions
* start of a table in the documentation to describe commonly used runtime attributes
* generate test benchmark data from results obtained with a 2 processor run - the same as what is done during the test
* relaxed tolerance on test
* regenerate CI test reference data with USE_PSATD=TRUE
* Update Docs/source/developers/particles.rst

Co-authored-by: Phil Miller <unmobile+gh@gmail.com>
Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

1 files changed, 35 insertions, 0 deletions

diff --git a/Source/Particles/PhysicalParticleContainer.cpp b/Source/Particles/PhysicalParticleContainer.cpp
index d489cddfe..c704e824a 100644
--- a/Source/Particles/PhysicalParticleContainer.cpp
+++ b/Source/Particles/PhysicalParticleContainer.cpp
@@ -230,6 +230,19 @@ PhysicalParticleContainer::PhysicalParticleContainer (AmrCore* amr_core, int isp
     }
 #endif
 
+    // If old particle positions should be saved add the needed components
+    pp_species_name.query("save_previous_position", m_save_previous_position);
+    if (m_save_previous_position) {
+        AddRealComp("prev_x");
+#if (AMREX_SPACEDIM == 3)
+        AddRealComp("prev_y");
+#endif
+        AddRealComp("prev_z");
+#ifdef WARPX_DIM_RZ
+      amrex::Abort("Saving previous particle positions not yet implemented in RZ");
+#endif
+    }
+
     // Get Galilean velocity
     ParmParse pp_psatd("psatd");
     bool use_default_v_galilean = false;
@@ -2317,6 +2330,20 @@ PhysicalParticleContainer::PushPX (WarpXParIter& pti,
         ion_lev = pti.GetiAttribs(particle_icomps["ionization_level"]).dataPtr();
     }
 
+    const bool save_previous_position = m_save_previous_position;
+    ParticleReal* x_old = nullptr;
+    ParticleReal* y_old = nullptr;
+    ParticleReal* z_old = nullptr;
+    if (save_previous_position) {
+        x_old = pti.GetAttribs(particle_comps["prev_x"]).dataPtr();
+#if (AMREX_SPACEDIM == 3)
+        y_old = pti.GetAttribs(particle_comps["prev_y"]).dataPtr();
+#else
+    amrex::ignore_unused(y_old);
+#endif
+        z_old = pti.GetAttribs(particle_comps["prev_z"]).dataPtr();
+    }
+
     // Loop over the particles and update their momentum
     const amrex::Real q = this->charge;
     const amrex::Real m = this-> mass;
@@ -2344,6 +2371,14 @@ PhysicalParticleContainer::PushPX (WarpXParIter& pti,
         amrex::ParticleReal xp, yp, zp;
         getPosition(ip, xp, yp, zp);
 
+        if (save_previous_position) {
+            x_old[ip] = xp;
+#if (AMREX_SPACEDIM == 3)
+            y_old[ip] = yp;
+#endif
+            z_old[ip] = zp;
+        }
+
         amrex::ParticleReal Exp = 0._rt, Eyp = 0._rt, Ezp = 0._rt;
         amrex::ParticleReal Bxp = 0._rt, Byp = 0._rt, Bzp = 0._rt;