From 1dde37bd56437f2a5aac7e607b8ea9f5b4c084a6 Mon Sep 17 00:00:00 2001
From: wearysebas <sebichito@gmail.com>
Date: Thu, 22 Jan 2026 15:58:33 +0000
Subject: [PATCH 1/2] Add checks to chooseProcessorSplit function in
 boutmesh.cxx

Setting NXPE or NYPE would not trigger the checks of number of points / number of specified processes. Also added tests to it and modified previous tests to work.
---
 src/mesh/impls/bout/boutmesh.cxx  | 14 ++++++++---
 tests/unit/mesh/test_boutmesh.cxx | 42 ++++++++++++++++++++++++++++---
 2 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/src/mesh/impls/bout/boutmesh.cxx b/src/mesh/impls/bout/boutmesh.cxx
index 4be01d4637..999120f48a 100644
--- a/src/mesh/impls/bout/boutmesh.cxx
+++ b/src/mesh/impls/bout/boutmesh.cxx
@@ -156,7 +156,7 @@ namespace bout {
 CheckMeshResult checkBoutMeshYDecomposition(int num_y_processors, int ny,
                                             int num_y_guards, int jyseps1_1,
                                             int jyseps2_1, int jyseps1_2, int jyseps2_2,
-                                            int ny_inner) {
+                                            int ny_inner) {                                       
 
   const int num_local_y_points = ny / num_y_processors;
 
@@ -245,7 +245,11 @@ void BoutMesh::chooseProcessorSplit(Options& options) {
           _("Number of processors ({:d}) not divisible by NPs in x direction ({:d})\n"),
           NPES, NXPE);
     }
-
+    if (nx % NXPE != 0) {
+      throw BoutException(
+          _("Number of x points ({:d}) not divisible by NPs in x direction ({:d})\n"), nx,
+          NXPE);
+    }
     NYPE = NPES / NXPE;
   } else {
     // NXPE not set, but NYPE is
@@ -258,7 +262,11 @@ void BoutMesh::chooseProcessorSplit(Options& options) {
           _("Number of processors ({:d}) not divisible by NPs in y direction ({:d})\n"),
           NPES, NYPE);
     }
-
+    if (ny % NYPE != 0) {
+      throw BoutException(
+          _("Number of y points ({:d}) not divisible by NPs in y direction ({:d})\n"), nx,
+          NXPE);
+    }
     NXPE = NPES / NYPE;
   }
 
diff --git a/tests/unit/mesh/test_boutmesh.cxx b/tests/unit/mesh/test_boutmesh.cxx
index 8a446a742b..45217bfbe0 100644
--- a/tests/unit/mesh/test_boutmesh.cxx
+++ b/tests/unit/mesh/test_boutmesh.cxx
@@ -464,7 +464,7 @@ TEST_P(BadBoutMeshDecompositionTest, BadSingleCoreYDecomposition) {
   EXPECT_THAT(result.reason, HasSubstr(params.expected_message));
 }
 
-TEST_F(BoutMeshTest, ChooseProcessorSplitBadNXPE) {
+TEST_F(BoutMeshTest, ChooseProcessorSplitBadNXPETooManyXProcs) {
   Options options{{"NXPE", 3}};
 
   BoutMeshExposer mesh(1, 24, 1, 1, 1, 8);
@@ -472,7 +472,7 @@ TEST_F(BoutMeshTest, ChooseProcessorSplitBadNXPE) {
   EXPECT_THROW(mesh.chooseProcessorSplit(options), BoutException);
 }
 
-TEST_F(BoutMeshTest, ChooseProcessorSplitBadNYPE) {
+TEST_F(BoutMeshTest, ChooseProcessorSplitBadNYPETooManyYProcs) {
   Options options{{"NYPE", 7}};
 
   BoutMeshExposer mesh(1, 24, 1, 1, 1, 8);
@@ -480,10 +480,46 @@ TEST_F(BoutMeshTest, ChooseProcessorSplitBadNYPE) {
   EXPECT_THROW(mesh.chooseProcessorSplit(options), BoutException);
 }
 
+TEST_F(BoutMeshTest, ChooseProcessorSplitBadNXPENotDivisibleByNYPE) {
+  WithQuietOutput info{output_info};
+  Options options{{"NXPE", 5}};
+
+  BoutMeshExposer mesh(5, 24, 1, 1, 1, 8);
+
+  EXPECT_THROW(mesh.chooseProcessorSplit(options), BoutException);
+}
+
+TEST_F(BoutMeshTest, ChooseProcessorSplitBadNYPENotDivisibleByNYPE) {
+  WithQuietOutput info{output_info};
+  Options options{{"NYPE", 5}};
+
+  BoutMeshExposer mesh(5, 5, 1, 1, 1, 8);
+
+  EXPECT_THROW(mesh.chooseProcessorSplit(options), BoutException);
+}
+
+TEST_F(BoutMeshTest, ChooseProcessorSplitBadNXPENotDivisibleByNYPE) {
+  WithQuietOutput info{output_info};
+  Options options{{"NXPE", 5}};
+
+  BoutMeshExposer mesh(5, 24, 1, 1, 1, 8);
+
+  EXPECT_THROW(mesh.chooseProcessorSplit(options), BoutException);
+}
+
+TEST_F(BoutMeshTest, ChooseProcessorSplitBadNYPENotDivisibleByNYPE) {
+  WithQuietOutput info{output_info};
+  Options options{{"NYPE", 5}};
+
+  BoutMeshExposer mesh(5, 5, 1, 1, 1, 8);
+
+  EXPECT_THROW(mesh.chooseProcessorSplit(options), BoutException);
+}
+
 TEST_F(BoutMeshTest, ChooseProcessorSplitNXPE) {
   Options options{{"NXPE", 4}};
 
-  BoutMeshExposer mesh(1, 24, 1, 1, 1, 8);
+  BoutMeshExposer mesh(4, 24, 1, 1, 1, 8);
 
   EXPECT_NO_THROW(mesh.chooseProcessorSplit(options));
 

From 3e54ba5977bf4b3f9cf37a57c3883c0cfa12c148 Mon Sep 17 00:00:00 2001
From: wearysebas <10083044+wearysebas@users.noreply.github.com>
Date: Thu, 29 Jan 2026 14:38:05 +0000
Subject: [PATCH 2/2] Apply clang-format changes

---
 src/mesh/impls/bout/boutmesh.cxx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mesh/impls/bout/boutmesh.cxx b/src/mesh/impls/bout/boutmesh.cxx
index 999120f48a..a0a4a611c4 100644
--- a/src/mesh/impls/bout/boutmesh.cxx
+++ b/src/mesh/impls/bout/boutmesh.cxx
@@ -156,7 +156,7 @@ namespace bout {
 CheckMeshResult checkBoutMeshYDecomposition(int num_y_processors, int ny,
                                             int num_y_guards, int jyseps1_1,
                                             int jyseps2_1, int jyseps1_2, int jyseps2_2,
-                                            int ny_inner) {                                       
+                                            int ny_inner) {
 
   const int num_local_y_points = ny / num_y_processors;