Fix `max_step` from `zmax_plasma...` upon restart (#3732)

* fix zmax_plasma_... calculation upon restart

* simple fix didn't work in all cases

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix indentation

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

1 files changed, 11 insertions, 5 deletions

diff --git a/Source/Initialization/WarpXInitData.cpp b/Source/Initialization/WarpXInitData.cpp
index 4622367a2..43bd597bd 100644
--- a/Source/Initialization/WarpXInitData.cpp
+++ b/Source/Initialization/WarpXInitData.cpp
@@ -375,6 +375,12 @@ WarpX::InitData ()
 
     Print() << utils::logo::get_logo();
 
+    // WarpX::computeMaxStepBoostAccelerator
+    // needs to start from the initial zmin_domain_boost,
+    // even if restarting from a checkpoint file
+    if (do_compute_max_step_from_zmax) {
+        zmin_domain_boost_step_0 = geom[0].ProbLo(WARPX_ZINDEX);
+    }
     if (restart_chkfile.empty())
     {
         ComputeDt();
@@ -549,7 +555,7 @@ void
 WarpX::ComputeMaxStep ()
 {
     if (do_compute_max_step_from_zmax) {
-        computeMaxStepBoostAccelerator(geom[0]);
+        computeMaxStepBoostAccelerator();
     }
 }
 
@@ -560,7 +566,7 @@ WarpX::ComputeMaxStep ()
  * simulation box passes input parameter zmax_plasma_to_compute_max_step.
  */
 void
-WarpX::computeMaxStepBoostAccelerator(const amrex::Geometry& a_geom){
+WarpX::computeMaxStepBoostAccelerator() {
     // Sanity checks: can use zmax_plasma_to_compute_max_step only if
     // the moving window and the boost are all in z direction.
     WARPX_ALWAYS_ASSERT_WITH_MESSAGE(
@@ -578,7 +584,7 @@ WarpX::computeMaxStepBoostAccelerator(const amrex::Geometry& a_geom){
 
     // Lower end of the simulation domain. All quantities are given in boosted
     // frame except zmax_plasma_to_compute_max_step.
-    const Real zmin_domain_boost = a_geom.ProbLo(WARPX_ZINDEX);
+
     // End of the plasma: Transform input argument
     // zmax_plasma_to_compute_max_step to boosted frame.
     const Real len_plasma_boost = zmax_plasma_to_compute_max_step/gamma_boost;
@@ -586,7 +592,7 @@ WarpX::computeMaxStepBoostAccelerator(const amrex::Geometry& a_geom){
     const Real v_plasma_boost = -beta_boost * PhysConst::c;
     // Get time at which the lower end of the simulation domain passes the
     // upper end of the plasma (in the z direction).
-    const Real interaction_time_boost = (len_plasma_boost-zmin_domain_boost)/
+    const Real interaction_time_boost = (len_plasma_boost-zmin_domain_boost_step_0)/
         (moving_window_v-v_plasma_boost);
     // Divide by dt, and update value of max_step.
     int computed_max_step;
@@ -598,7 +604,7 @@ WarpX::computeMaxStepBoostAccelerator(const amrex::Geometry& a_geom){
     }
     max_step = computed_max_step;
     Print()<<"max_step computed in computeMaxStepBoostAccelerator: "
-           <<computed_max_step<<std::endl;
+           <<max_step<<std::endl;
 }
 
 void