Add support for uniform grid sizing across subdomains (#720) (#5253)

Co-authored-by: Valentin Sulzer <[email protected]>

Author: 2 people

CHANGELOG.md

@@ -24,6 +24,7 @@
 
 ## Features
 
+- Added uniform grid sizing across subdomains in the x-dimension, ensuring consistent grid spacing when geometries have varying lengths. ([#5253](https://github.com/pybamm-team/PyBaMM/pull/5253))
 - Added the `electrode_phases` kwarg to `plot_voltage_components()` which allows choosing between plotting primary or secondary phase overpotentials. ([#5229](https://github.com/pybamm-team/PyBaMM/pull/5229))
 - Added the `num_steps_no_progress` and `t_no_progress` options in the `IDAKLUSolver` to early terminate the simulation if little progress is detected. ([#5201](https://github.com/pybamm-team/PyBaMM/pull/5201))
 - EvaluateAt symbol: add support for children evaluated at edges ([#5190](https://github.com/pybamm-team/PyBaMM/pull/5190))

src/pybamm/meshes/meshes.py

@@ -9,6 +9,39 @@
 import pybamm
 
 
+def compute_var_pts_from_thicknesses(electrode_thicknesses, grid_size):
+    """
+    Compute a ``var_pts`` dictionary using electrode thicknesses and a target cell size (dx).
+
+    Added as per maintainer feedback in issue #<your-issue-number> to make mesh generation
+    explicit — ``grid_size`` now represents the mesh cell size in metres.
+
+    Parameters
+    ----------
+    electrode_thicknesses : dict
+        Domain thicknesses in metres.
+    grid_size : float
+        Desired uniform mesh cell size (m).
+
+    Returns
+    -------
+    dict
+        Mapping of each domain to its computed grid points.
+    """
+    if not isinstance(electrode_thicknesses, dict):
+        raise TypeError("electrode_thicknesses must be a dictionary")
+
+    if not isinstance(grid_size, (int | float)) or grid_size <= 0:
+        raise ValueError("grid_size must be a positive number")
+
+    var_pts = {}
+    for domain, thickness in electrode_thicknesses.items():
+        npts = max(round(thickness / grid_size), 2)
+        var_pts[domain] = {f"x_{domain[0]}": npts}
+
+    return var_pts
+
+
 class Mesh(dict):
     """
     Mesh contains a list of submeshes on each subdomain.

tests/unit/test_meshes/test_meshes.py

@@ -584,6 +584,37 @@ def test_to_json(self):
 
         assert mesh_json == expected_json
 
+    def test_compute_var_pts_from_thicknesses_cell_size(self):
+        from pybamm.meshes.meshes import compute_var_pts_from_thicknesses
+
+        electrode_thicknesses = {
+            "negative electrode": 100e-6,
+            "separator": 25e-6,
+            "positive electrode": 100e-6,
+        }
+
+        cell_size = 5e-6  # 5 micrometres per cell
+        var_pts = compute_var_pts_from_thicknesses(electrode_thicknesses, cell_size)
+
+        assert isinstance(var_pts, dict)
+        assert all(isinstance(v, dict) for v in var_pts.values())
+        assert var_pts["negative electrode"]["x_n"] == 20
+        assert var_pts["separator"]["x_s"] == 5
+        assert var_pts["positive electrode"]["x_p"] == 20
+
+    def test_compute_var_pts_from_thicknesses_invalid_thickness_type(self):
+        from pybamm.meshes.meshes import compute_var_pts_from_thicknesses
+
+        with pytest.raises(TypeError):
+            compute_var_pts_from_thicknesses(["not", "a", "dict"], 1e-6)
+
+    def test_compute_var_pts_from_thicknesses_invalid_grid_size(self):
+        from pybamm.meshes.meshes import compute_var_pts_from_thicknesses
+
+        electrode_thicknesses = {"negative electrode": 100e-6}
+        with pytest.raises(ValueError):
+            compute_var_pts_from_thicknesses(electrode_thicknesses, -1e-6)
+
 
 class TestMeshGenerator:
     def test_init_name(self):