From 7c71053b752840cc43c7b899ae1dacfd85f4f318 Mon Sep 17 00:00:00 2001
From: Dilan Pathirana <59329744+dilpath@users.noreply.github.com>
Date: Mon, 20 Nov 2023 12:06:22 +0100
Subject: [PATCH] Fix multi-subspace stepwise moves (#65)

---
 petab_select/model_subspace.py | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/petab_select/model_subspace.py b/petab_select/model_subspace.py
index 8c0281d5..9b40f696 100644
--- a/petab_select/model_subspace.py
+++ b/petab_select/model_subspace.py
@@ -232,8 +232,10 @@ def continue_searching(
         if candidate_space.predecessor_model == VIRTUAL_INITIAL_MODEL:
             if candidate_space.method == Method.FORWARD:
                 old_estimated_all = set()
+                old_fixed_all = set(self.parameters)
             elif candidate_space.method == Method.BACKWARD:
                 old_estimated_all = set(self.parameters)
+                old_fixed_all = set()
             else:
                 # Should already be handled elsewhere (e.g.
                 # `self.check_compatibility_stepwise_method`).
@@ -242,10 +244,16 @@ def continue_searching(
                 )
         else:
             old_estimated_all = set()
+            old_fixed_all = set()
             if isinstance(candidate_space.predecessor_model, Model):
                 old_estimated_all = (
                     candidate_space.predecessor_model.get_estimated_parameter_ids_all()
                 )
+                old_fixed_all = [
+                    parameter_id
+                    for parameter_id in self.parameters_all
+                    if parameter_id not in old_estimated_all
+                ]
 
         # Parameters that are fixed in the candidate space
         # predecessor model but are necessarily estimated in this subspace.
@@ -264,6 +272,7 @@ def continue_searching(
 
         # Parameters related to minimal changes compared to the predecessor model.
         old_estimated = set(old_estimated_all).intersection(self.can_estimate)
+        old_fixed = set(old_fixed_all).intersection(self.can_fix)
         new_must_estimate = set(new_must_estimate_all).intersection(
             self.parameters
         )
@@ -304,14 +313,14 @@ def continue_searching(
                 new_must_estimate_all
                 or candidate_space.predecessor_model == VIRTUAL_INITIAL_MODEL
             ):
-                # Consider minimal models that have all necessary parameters
-                # estimated. As this subspace necessarily has more estimated
-                # parameters than the predecessor model, all parameters that
-                # can be fixed, will be fixed.
+                # Consider minimal models that have all necessarily-estimated
+                # parameters.
                 estimated_parameters = {
                     parameter_id: ESTIMATE
-                    for parameter_id in set(self.parameters).difference(
-                        self.can_fix
+                    for parameter_id in (
+                        set(self.parameters)
+                        .difference(self.can_fix)
+                        .union(old_estimated)
                     )
                 }
                 models = self.get_models(
@@ -394,14 +403,14 @@ def continue_searching(
                 new_must_fix_all
                 or candidate_space.predecessor_model == VIRTUAL_INITIAL_MODEL
             ):
-                # Consider minimal models that have all necessarily fixed parameters.
-                # As this subspace necessarily has fewer estimated parameters than the
-                # predecessor model, all parameters that can be estimated, will be
-                # estimated.
+                # Consider minimal models that have all necessarily-fixed
+                # parameters.
                 estimated_parameters = {
                     parameter_id: ESTIMATE
-                    for parameter_id in set(self.parameters).difference(
-                        self.must_fix
+                    for parameter_id in (
+                        set(self.parameters)
+                        .difference(self.must_fix)
+                        .difference(old_fixed)
                     )
                 }
                 models = self.get_models(