From 8f506de1d7ad87b510a68f7e9fa6b4c459a5e08b Mon Sep 17 00:00:00 2001
From: Alex Dowling <adowling@nd.edu>
Date: Mon, 22 Jun 2026 11:55:54 -0400
Subject: [PATCH] Bug fix: SSE_weighted should support heterogenous measurement
 errors

---
 pyomo/contrib/parmest/parmest.py            | 32 +++++++++++---
 pyomo/contrib/parmest/tests/test_parmest.py | 46 +++++++++++++++++++++
 2 files changed, 73 insertions(+), 5 deletions(-)

diff --git a/pyomo/contrib/parmest/parmest.py b/pyomo/contrib/parmest/parmest.py
index 6e6d040b792..af79bb8a19e 100644
--- a/pyomo/contrib/parmest/parmest.py
+++ b/pyomo/contrib/parmest/parmest.py
@@ -447,7 +447,13 @@ def validate_experiment_outputs(output_vars):
             ), "Experiment outputs must share the same indices or data points"
 
 
-def _count_total_experiments(experiment_list):
+def _all_measurement_errors_known(model):
+    return hasattr(model, "measurement_error") and all(
+        model.measurement_error[y_hat] is not None for y_hat in model.experiment_outputs
+    )
+
+
+def _count_total_experiments(experiment_list, require_uniform_output_grid=True):
     """
     Counts the number of data points in the list of experiments
 
@@ -474,6 +480,10 @@ def _count_total_experiments(experiment_list):
     experiment_list : list
         List of Experiment class objects containing the Pyomo model
         for the different experimental conditions
+    require_uniform_output_grid : bool, optional
+        If True, validate that all output families within an experiment share
+        the same number of indices and the same indices before counting data
+        points. Default is True.
 
     Returns
     -------
@@ -488,7 +498,8 @@ def _count_total_experiments(experiment_list):
         output_vars = model.experiment_outputs
 
         # check if the experiment outputs are defined correctly
-        validate_experiment_outputs(output_vars)
+        if require_uniform_output_grid:
+            validate_experiment_outputs(output_vars)
 
         # store the indices of the experiment outputs
         indices = []
@@ -1074,9 +1085,6 @@ def __init__(
         assert isinstance(experiment_list, list)
         self.exp_list = experiment_list
 
-        # get the number of experiments
-        self.number_exp = _count_total_experiments(self.exp_list)
-
         # check if the experiment has a ``get_labeled_model`` function
         model = _get_labeled_model(self.exp_list[0])
 
@@ -1095,6 +1103,20 @@ def __init__(
         else:
             self.obj_function = obj_function
 
+        allow_heterogeneous_output_grids = (
+            self.obj_function == ObjectiveType.SSE_weighted
+            and all(
+                _all_measurement_errors_known(_get_labeled_model(experiment))
+                for experiment in self.exp_list
+            )
+        )
+
+        # get the number of experiments
+        self.number_exp = _count_total_experiments(
+            self.exp_list,
+            require_uniform_output_grid=not allow_heterogeneous_output_grids,
+        )
+
         if isinstance(regularization, str):
             try:
                 self.regularization = RegularizationType(regularization)
diff --git a/pyomo/contrib/parmest/tests/test_parmest.py b/pyomo/contrib/parmest/tests/test_parmest.py
index f44331a86ac..63cd1694ead 100644
--- a/pyomo/contrib/parmest/tests/test_parmest.py
+++ b/pyomo/contrib/parmest/tests/test_parmest.py
@@ -2173,6 +2173,42 @@ def get_labeled_model(self):
         return self.model
 
 
+class HeterogeneousOutputExperiment(Experiment):
+    def get_labeled_model(self):
+        m = pyo.ConcreteModel()
+
+        # Two measured output families intentionally use different time grids.
+        m.t1 = pyo.Set(initialize=[0.0, 1.0, 2.0])
+        m.t2 = pyo.Set(initialize=[0.0, 2.0])
+
+        m.y1 = pyo.Var(m.t1, initialize=1.0)
+        m.y2 = pyo.Var(m.t2, initialize=2.0)
+
+        m.theta = pyo.Var(initialize=1.0)
+        m.theta.fix(1.0)
+
+        m.experiment_outputs = pyo.Suffix(direction=pyo.Suffix.LOCAL)
+        m.measurement_error = pyo.Suffix(direction=pyo.Suffix.LOCAL)
+        m.unknown_parameters = pyo.Suffix(direction=pyo.Suffix.LOCAL)
+
+        y1_data = {0.0: 1.1, 1.0: 1.2, 2.0: 1.3}
+        y2_data = {0.0: 2.1, 2.0: 2.3}
+
+        for t in m.t1:
+            m.experiment_outputs[m.y1[t]] = y1_data[t]
+            m.measurement_error[m.y1[t]] = 0.1
+
+        for t in m.t2:
+            m.experiment_outputs[m.y2[t]] = y2_data[t]
+            m.measurement_error[m.y2[t]] = 0.2
+
+        # All measurement errors are supplied, so SSE_weighted should accept
+        # these heterogeneous output grids.
+        m.unknown_parameters[m.theta] = pyo.ComponentUID(m.theta)
+
+        return m
+
+
 def _build_estimator(data, include_second_output=False):
     exp_list = [
         LinearThetaExperiment(x=x, y=y, include_second_output=include_second_output)
@@ -2442,6 +2478,16 @@ def test_count_total_experiments_rejects_time_not_in_first_index(self):
         ):
             parmest._count_total_experiments(exp_list)
 
+    def test_estimator_accepts_sse_weighted_heterogeneous_outputs(self):
+        # Regression test for heterogeneous experiment outputs with complete
+        # measurement_error data under the SSE_weighted objective.
+        pest = parmest.Estimator(
+            [HeterogeneousOutputExperiment()], obj_function="SSE_weighted"
+        )
+
+        # Constructor success is the behavior under test.
+        self.assertIsInstance(pest, parmest.Estimator)
+
 
 ###########################
 # tests for deprecated UI #