From 244583587cc2d2fcb375831dc721e87d63387e22 Mon Sep 17 00:00:00 2001
From: wpbonelli <wbonelli@ucar.edu>
Date: Wed, 8 Jan 2025 18:46:05 -0500
Subject: [PATCH] fix(prt): don't reset transform in subcell rect method
 (#2131)

#2066 introduced a bug where particle coordinates were prematurely transformed back from cell-local coords to model coords. This produced incorrect particle positions in/near quad-refined cells.
---
 src/Solution/ParticleTracker/CellDefn.f90             |  2 --
 src/Solution/ParticleTracker/Method.f90               |  3 +--
 src/Solution/ParticleTracker/MethodDisv.f90           | 11 ++++++++++-
 src/Solution/ParticleTracker/MethodSubcellPollock.f90 |  1 -
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/Solution/ParticleTracker/CellDefn.f90 b/src/Solution/ParticleTracker/CellDefn.f90
index 836f0421633..a2f0fd5c5f4 100644
--- a/src/Solution/ParticleTracker/CellDefn.f90
+++ b/src/Solution/ParticleTracker/CellDefn.f90
@@ -1,7 +1,5 @@
 module CellDefnModule
   use KindModule, only: DP, I4B, LGP
-  use ConstantsModule, only: DZERO
-  use MathUtilModule, only: is_close
   implicit none
 
   private
diff --git a/src/Solution/ParticleTracker/Method.f90 b/src/Solution/ParticleTracker/Method.f90
index 061a627e1ad..4035a0ad8a1 100644
--- a/src/Solution/ParticleTracker/Method.f90
+++ b/src/Solution/ParticleTracker/Method.f90
@@ -134,9 +134,8 @@ subroutine try_pass(this, particle, nextlevel, advancing)
       ! otherwise pass the particle to the next subdomain.
       ! if that leaves it on a boundary, stop advancing.
       call this%pass(particle)
-      if (particle%iboundary(nextlevel - 1) .ne. 0) then
+      if (particle%iboundary(nextlevel - 1) .ne. 0) &
         advancing = .false.
-      end if
     end if
   end subroutine try_pass
 
diff --git a/src/Solution/ParticleTracker/MethodDisv.f90 b/src/Solution/ParticleTracker/MethodDisv.f90
index de65bbbf134..d6fefc4118a 100644
--- a/src/Solution/ParticleTracker/MethodDisv.f90
+++ b/src/Solution/ParticleTracker/MethodDisv.f90
@@ -88,6 +88,8 @@ subroutine load_disv(this, particle, next_level, submethod)
       ic = particle%idomain(next_level)
       call this%load_cell_defn(ic, cell%defn)
       if (this%fmi%ibdgwfsat0(ic) == 0) then
+        ! Cell is active but dry, so select and initialize pass-to-bottom
+        ! cell method and set cell method pointer
         call method_cell_ptb%init( &
           fmi=this%fmi, &
           cell=this%cell, &
@@ -95,6 +97,7 @@ subroutine load_disv(this, particle, next_level, submethod)
           tracktimes=this%tracktimes)
         submethod => method_cell_ptb
       else if (particle%ifrctrn > 0) then
+        ! Force the ternary method
         call method_cell_tern%init( &
           fmi=this%fmi, &
           cell=this%cell, &
@@ -102,6 +105,8 @@ subroutine load_disv(this, particle, next_level, submethod)
           tracktimes=this%tracktimes)
         submethod => method_cell_tern
       else if (cell%defn%can_be_rect) then
+        ! Cell is a rectangle, convert it to a rectangular cell type and
+        ! initialize Pollock's method
         call cell_poly_to_rect(cell, rect)
         base => rect
         call method_cell_plck%init( &
@@ -111,6 +116,8 @@ subroutine load_disv(this, particle, next_level, submethod)
           tracktimes=this%tracktimes)
         submethod => method_cell_plck
       else if (cell%defn%can_be_quad) then
+        ! Cell is quad-refined, convert to a quad rect cell type and
+        ! initialize the corresponding method
         call cell_poly_to_quad(cell, quad)
         base => quad
         call method_cell_quad%init( &
@@ -120,6 +127,7 @@ subroutine load_disv(this, particle, next_level, submethod)
           tracktimes=this%tracktimes)
         submethod => method_cell_quad
       else
+        ! Default to the ternary method
         call method_cell_tern%init( &
           fmi=this%fmi, &
           cell=this%cell, &
@@ -232,7 +240,8 @@ subroutine pass_disv(this, particle)
         particle%advancing = .false.
         call this%save(particle, reason=3)
       else
-        ! Update old to new cell properties
+        ! Otherwise, load cell properties into the
+        ! particle. It may be marked to terminate.
         call this%load_particle(cell, particle)
         if (.not. particle%advancing) return
 
diff --git a/src/Solution/ParticleTracker/MethodSubcellPollock.f90 b/src/Solution/ParticleTracker/MethodSubcellPollock.f90
index 1cbd0cce45b..55e8989a925 100644
--- a/src/Solution/ParticleTracker/MethodSubcellPollock.f90
+++ b/src/Solution/ParticleTracker/MethodSubcellPollock.f90
@@ -73,7 +73,6 @@ subroutine apply_msp(this, particle, tmax)
       call particle%transform(xOrigin, yOrigin)
       call this%track_subcell(subcell, particle, tmax)
       call particle%transform(xOrigin, yOrigin, invert=.true.)
-      call particle%reset_transform()
     end select
   end subroutine apply_msp