I would propose these changes

Author: panquez

src/geode/mesh/helpers/build_grid.cpp

@@ -27,7 +27,6 @@
 
 namespace geode
 {
-
     template < index_t dimension >
     LightRegularGrid< dimension >
         build_grid_from_bbox_target_length_and_maximum_cell_number(
@@ -41,22 +40,17 @@ namespace geode
         {
             numerator *= diagonal.value( d );
         }
-        const auto min_length =
-            std::pow( numerator / ( max_nb_cells - 1 ), 1. / dimension );
-        auto min_cell_length = min_length;
-        for( const auto d : LRange{ dimension } )
-        {
-            min_cell_length = std::max( ( diagonal.value( d ) + 2 * min_length )
-                                            / diagonal.value( d ) * min_length,
-                min_cell_length );
-        }
+        const auto min_cell_length =
+            std::pow( numerator / max_nb_cells, 1. / dimension );
         const auto cell_length =
             std::max( min_cell_length, target_cell_length );
         std::array< index_t, dimension > cell_numbers;
         std::array< double, dimension > cell_lengths;
         for( const auto d : LRange{ dimension } )
         {
-            cell_numbers[d] = std::ceil( diagonal.value( d ) / cell_length );
+            cell_numbers[d] = std::max( static_cast< index_t >( 1 ),
+                static_cast< index_t >(
+                    std::floor( diagonal.value( d ) / cell_length ) ) );
             cell_lengths[d] = diagonal.value( d ) / cell_numbers[d];
         }
         return { bbox.min(), std::move( cell_numbers ),

tests/mesh/CMakeLists.txt

@@ -275,3 +275,10 @@ add_geode_test(
         ${PROJECT_NAME}::geometry
         ${PROJECT_NAME}::mesh
 )
+add_geode_test(
+    SOURCE "test-build-grid.cpp"
+    DEPENDENCIES
+        ${PROJECT_NAME}::basic
+        ${PROJECT_NAME}::geometry
+        ${PROJECT_NAME}::mesh
+)

tests/mesh/test-build-grid.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2019 - 2024 Geode-solutions
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <geode/basic/logger.h>
+
+#include <geode/geometry/bounding_box.h>
+#include <geode/geometry/point.h>
+
+#include <geode/mesh/helpers/build_grid.h>
+
+#include <geode/tests/common.h>
+
+void test()
+{
+    geode::OpenGeodeMeshLibrary::initialize();
+    const geode::index_t max_nb_cells{ 100 };
+    geode::BoundingBox2D bbox;
+    bbox.add_point( { { 0, 0 } } );
+    bbox.add_point( { { 1, 1 } } );
+    const auto grid =
+        geode::build_grid_from_bbox_target_length_and_maximum_cell_number(
+            bbox, 0.01, max_nb_cells );
+    DEBUG( grid.nb_cells() );
+    DEBUG( grid.nb_cells_in_direction( 0 ) );
+    DEBUG( grid.nb_cells_in_direction( 1 ) );
+    DEBUG( grid.cell_length_in_direction( 0 ) );
+    DEBUG( grid.cell_length_in_direction( 1 ) );
+    OPENGEODE_EXCEPTION( grid.nb_cells() <= max_nb_cells,
+        "[Test] Too much cells in built grid" );
+
+    bbox.add_point( { { 1, 10 } } );
+    const auto grid2 =
+        geode::build_grid_from_bbox_target_length_and_maximum_cell_number(
+            bbox, 0.01, max_nb_cells );
+    DEBUG( grid2.nb_cells() );
+    DEBUG( grid2.nb_cells_in_direction( 0 ) );
+    DEBUG( grid2.nb_cells_in_direction( 1 ) );
+    DEBUG( grid2.cell_length_in_direction( 0 ) );
+    DEBUG( grid2.cell_length_in_direction( 1 ) );
+    OPENGEODE_EXCEPTION( grid.nb_cells() <= max_nb_cells,
+        "[Test] Too much cells in built grid2" );
+
+    bbox.add_point( { { 3, 10 } } );
+    const auto grid3 =
+        geode::build_grid_from_bbox_target_length_and_maximum_cell_number(
+            bbox, 0.01, max_nb_cells );
+    DEBUG( grid3.nb_cells() );
+    DEBUG( grid3.nb_cells_in_direction( 0 ) );
+    DEBUG( grid3.nb_cells_in_direction( 1 ) );
+    DEBUG( grid3.cell_length_in_direction( 0 ) );
+    DEBUG( grid3.cell_length_in_direction( 1 ) );
+    OPENGEODE_EXCEPTION( grid.nb_cells() <= max_nb_cells,
+        "[Test] Too much cells in built grid3" );
+}
+
+OPENGEODE_TEST( "graph" )