Restore ordering of w (#3051)

With #3036, the ordering of `w` symbols and expressions has changed.
This is not a problem per se, but would require recreating the
test oracles for the models in `models/`.
Therefore, don't do any unnecessary reordering.

Author: dweindl

python/sdist/amici/de_model.py

@@ -2588,27 +2588,19 @@ def has_event_assignments(self) -> bool:
         """
         return any(event.updates_state for event in self._events)
 
-    def toposort_expressions(self) -> dict[sp.Symbol, sp.Expr]:
+    def toposort_expressions(
+        self, reorder: bool = True
+    ) -> dict[sp.Symbol, sp.Expr]:
         """
         Sort expressions in topological order.
 
+        :param reorder:
+            Whether to reorder the internal expression list (``True``) or
+            just return the toposorted expressions (``False``).
+
         :return:
             dict of expression symbols to expressions in topological order
         """
-        # ensure no symbols or equations that depend on `w` have been generated
-        #  yet, otherwise the re-ordering might break dependencies
-        if (
-            generated := set(self._syms)
-            | set(self._eqs)
-            | set(self._sparsesyms)
-            | set(self._sparseeqs)
-        ) - {"w", "p", "k", "x", "x_rdata"}:
-            raise AssertionError(
-                "This function must be called before computing any "
-                "derivatives. The following symbols/equations are already "
-                f"generated: {generated}"
-            )
-
         # NOTE: elsewhere, conservations law expressions are expected to
         #  occur before any other w expressions, so we must maintain their
         #  position.
@@ -2627,6 +2619,23 @@ def toposort_expressions(self) -> dict[sp.Symbol, sp.Expr]:
             for e in self.expressions()[: self.num_cons_law()]
         } | w_toposorted
 
+        if not reorder:
+            return w_toposorted
+
+        # ensure no symbols or equations that depend on `w` have been generated
+        #  yet, otherwise the re-ordering might break dependencies
+        if (
+            generated := set(self._syms)
+            | set(self._eqs)
+            | set(self._sparsesyms)
+            | set(self._sparseeqs)
+        ) - {"w", "p", "k", "x", "x_rdata"}:
+            raise AssertionError(
+                "This function must be called before computing any "
+                "derivatives. The following symbols/equations are already "
+                f"generated: {generated}"
+            )
+
         old_syms = tuple(e.get_sym() for e in self.expressions())
         topo_expr_syms = tuple(w_toposorted)
         new_order = [old_syms.index(s) for s in topo_expr_syms]

python/sdist/amici/importers/sbml/__init__.py

@@ -3094,11 +3094,20 @@ def do_subs(expr, rate_ofs) -> sp.Expr:
 
         # replace rateOf-instances in expressions which we will need for
         #  substitutions later
+        expressions_changed = False
         for expr in de_model.expressions():
             if rate_ofs := expr.get_val().find(rate_of_func):
                 expr.set_val(do_subs(expr.get_val(), rate_ofs))
-
-        w_toposorted = de_model.toposort_expressions()
+                expressions_changed = True
+
+        # get toposorted `w`, but only changed the order of expressions in the
+        #  model if any expression changed.
+        # (in principle, we could always reorder the expressions, but this
+        #  will require regenerating all test oracle for
+        #  `test_pregenerated_models.py`)
+        w_toposorted = de_model.toposort_expressions(
+            reorder=expressions_changed
+        )
 
         # replace rateOf-instances in x0
         # indices of state variables whose x0 was modified