From 4018cb975abf3e72c2156366962c9dff7e9e961b Mon Sep 17 00:00:00 2001
From: danieljvickers <dnlvickers5@gmail.com>
Date: Wed, 17 Jun 2026 15:54:49 -0400
Subject: [PATCH] Fixed an edge case in periodic bounds checking for
 neighborhood size where the beginning and ending of a domain would be equal
 to each other

---
 src/simulation/m_start_up.fpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/simulation/m_start_up.fpp b/src/simulation/m_start_up.fpp
index 4651133b83..6bb59e7a64 100644
--- a/src/simulation/m_start_up.fpp
+++ b/src/simulation/m_start_up.fpp
@@ -1494,6 +1494,13 @@ contains
                     call MPI_SENDRECV(end_val, 1, mpi_p, send_neighbor, ${TAG + 1}$, recv_val, 1, mpi_p, recv_neighbor, &
                                       & ${TAG + 1}$, MPI_COMM_WORLD, MPI_STATUS_IGNORE, ierr)
                     end_val = recv_val
+
+                    ! protect from looping back around on yourself multiple times
+                    if (f_approx_equal(beg_val, ${X}$_cb(${DIM}$)) .or. f_approx_equal(end_val, ${X}$_cb(-1))) then
+                        beg_val = -huge(0._wp)
+                        end_val = huge(0._wp)
+                        exit
+                    end if
                 end do
                 neighbor_domain_${X}$%beg = beg_val
                 neighbor_domain_${X}$%end = end_val