Observe 0D custom variables after solving

.github/workflows/benchmark_on_push.yml

@@ -40,7 +40,7 @@ jobs:
           enable-cache: true
 
       - name: Install python dependencies
-        run: uv pip install asv[virtualenv]
+        run: uv pip install --system asv
 
       - name: Fetch base branch
         run: |

.github/workflows/periodic_benchmarks.yml

@@ -48,7 +48,7 @@ jobs:
           enable-cache: true
 
       - name: Install python dependencies
-        run: uv pip install asv[virtualenv]
+        run: uv pip install --system asv
 
       - name: Run benchmarks
         run: |

CHANGELOG.md

@@ -2,8 +2,14 @@
 
 ## Features
 
+- Adds the ability to observe custom 0D variables from a `Solution` object. ([#5308](https://github.com/pybamm-team/PyBaMM/pull/5308))
+- Adds `silence_sundials_errors` IDAKLU solver option with `default=False` to match historical output. ([#5290](https://github.com/pybamm-team/PyBaMM/pull/5290))
+
 ## Bug fixes
 
+- Fixed a bug where `IDAKLUSolver` errors were not raised correctly. ([#5291](https://github.com/pybamm-team/PyBaMM/pull/5291))
+- Fix a bug with serialising `InputParameter`s. ([#5289](https://github.com/pybamm-team/PyBaMM/pull/5289))
+
 # [v25.10.1](https://github.com/pybamm-team/PyBaMM/tree/v25.10.1) - 2025-11-14
 
 ## Features
@@ -19,6 +25,7 @@
 
 ## 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))

docs/source/api/expression_tree/operations/index.rst

@@ -10,3 +10,4 @@ Classes and functions that operate on the expression tree
   convert_to_casadi
   serialise
   unpack_symbol
+  replace_symbols

docs/source/api/expression_tree/operations/replace_symbols.rst

@@ -0,0 +1,11 @@
+Symbol Replacer
+================
+
+.. autoclass:: pybamm.SymbolReplacer
+  :members:
+
+Variable Replacement Map
+=========================
+
+.. autoclass:: pybamm.VariableReplacementMap
+  :members:

docs/source/examples/notebooks/creating_models/4-comparing-full-and-reduced-order-models.ipynb

@@ -24,7 +24,7 @@
     "$$\n",
     "\\left.c\\right\\vert_{t=0} = c_0,\n",
     "$$\n",
-    "where $c$$ is the concentration, $r$ the radial coordinate, $t$ time, $R$ the particle radius, $D$ the diffusion coefficient, $j$ the interfacial current density, $F$ Faraday's constant, and $c_0$ the initial concentration. \n",
+    "where $c$ is the concentration, $r$ the radial coordinate, $t$ time, $R$ the particle radius, $D$ the diffusion coefficient, $j$ the interfacial current density, $F$ Faraday's constant, and $c_0$ the initial concentration. \n",
     "\n",
     "As in the previous example we use the following parameters:\n",
     "\n",

pyproject.toml

@@ -25,7 +25,7 @@ classifiers = [
     "Topic :: Scientific/Engineering",
 ]
 dependencies = [
-    "pybammsolvers>=0.3.0,<0.4.0",
+    "pybammsolvers>=0.3.3,<0.4.0",
     "black",
     "numpy",
     "scipy>=1.11.4",

src/pybamm/__init__.py

@@ -59,6 +59,10 @@
 from .expression_tree.operations.convert_to_casadi import CasadiConverter
 from .expression_tree.operations.unpack_symbols import SymbolUnpacker
 from .expression_tree.operations.serialise import Serialise,ExpressionFunctionParameter
+from .expression_tree.operations.replace_symbols import (
+    SymbolReplacer,
+    VariableReplacementMap,
+)
 
 # Model classes
 from .models.base_model import BaseModel

src/pybamm/discretisations/discretisation.py

@@ -800,34 +800,32 @@ def process_symbol(self, symbol):
             Discretised symbol
 
         """
-        try:
-            return self._discretised_symbols[symbol]
-        except KeyError:
-            discretised_symbol = self._process_symbol(symbol)
-            self._discretised_symbols[symbol] = discretised_symbol
-            discretised_symbol.test_shape()
-
-            # Assign mesh as an attribute to the processed variable
-            if symbol.domain != []:
-                discretised_symbol.mesh = self.mesh[symbol.domain]
-            else:
-                discretised_symbol.mesh = None
+        _discretised_symbol = self._discretised_symbols.get(symbol)
+        if _discretised_symbol is not None:
+            return _discretised_symbol
+        discretised_symbol = self._process_symbol(symbol)
+        self._discretised_symbols[symbol] = discretised_symbol
+        discretised_symbol.test_shape()
+
+        # Assign mesh as an attribute to the processed variable
+        if symbol.domain != []:
+            discretised_symbol.mesh = self.mesh[symbol.domain]
+        else:
+            discretised_symbol.mesh = None
 
-            # Assign secondary mesh
-            if symbol.domains["secondary"] != []:
-                discretised_symbol.secondary_mesh = self.mesh[
-                    symbol.domains["secondary"]
-                ]
-            else:
-                discretised_symbol.secondary_mesh = None
+        # Assign secondary mesh
+        if symbol.domains["secondary"] != []:
+            discretised_symbol.secondary_mesh = self.mesh[symbol.domains["secondary"]]
+        else:
+            discretised_symbol.secondary_mesh = None
 
-            # Assign tertiary mesh
-            if symbol.domains["tertiary"] != []:
-                discretised_symbol.tertiary_mesh = self.mesh[symbol.domains["tertiary"]]
-            else:
-                discretised_symbol.tertiary_mesh = None
+        # Assign tertiary mesh
+        if symbol.domains["tertiary"] != []:
+            discretised_symbol.tertiary_mesh = self.mesh[symbol.domains["tertiary"]]
+        else:
+            discretised_symbol.tertiary_mesh = None
 
-            return discretised_symbol
+        return discretised_symbol
 
     def _process_symbol(self, symbol):
         """See :meth:`Discretisation.process_symbol()`."""
@@ -841,15 +839,13 @@ def _process_symbol(self, symbol):
                     self.bcs[key_id] = self.check_tab_conditions(
                         symbol, self.bcs[key_id]
                     )
+        else:
+            spatial_method = None
 
         if isinstance(symbol, pybamm.BinaryOperator):
             # Pre-process children
             left, right = symbol.children
             # Catch case where diffusion is a scalar and turn it into an identity matrix vector field.
-            if len(symbol.domain) != 0:
-                spatial_method = self.spatial_methods[symbol.domain[0]]
-            else:
-                spatial_method = None
             if isinstance(spatial_method, pybamm.FiniteVolume2D):
                 if isinstance(left, pybamm.Scalar) and (
                     isinstance(right, pybamm.VectorField)

src/pybamm/expression_tree/operations/convert_to_casadi.py

@@ -46,15 +46,15 @@ def convert(
         :class:`casadi.MX`
             The converted symbol
         """
-        try:
-            return self._casadi_symbols[symbol]
-        except KeyError:
-            # Change inputs to empty dictionary if it's None
-            inputs = inputs or {}
-            casadi_symbol = self._convert(symbol, t, y, y_dot, inputs)
-            self._casadi_symbols[symbol] = casadi_symbol
+        _casadi_symbol = self._casadi_symbols.get(symbol)
+        if _casadi_symbol is not None:
+            return _casadi_symbol
+        # Change inputs to empty dictionary if it's None
+        inputs = inputs or {}
+        casadi_symbol = self._convert(symbol, t, y, y_dot, inputs)
+        self._casadi_symbols[symbol] = casadi_symbol
 
-            return casadi_symbol
+        return casadi_symbol
 
     def _convert(self, symbol, t, y, y_dot, inputs):
         """See :meth:`CasadiConverter.convert()`."""