Params indexed by ContinuousSets are not initialized when the set is discretized.

[dallan-keylogic]

Summary

When a Param is indexed by a ContinuousSet and that ContinuousSet is discretize, the Param is not initialized on the new indices created. If the Param is mutable and initialized at some value, I would expect the new ParamData to be initialized at the same value. If it's not mutable, then I'd expect either indexing it by a ContinuousSet or discretizing that ContinuousSet to fail.

Steps to reproduce the issue

import pyomo.environ as pyo
from pyomo.dae import DerivativeVar, ContinuousSet

m = pyo.ConcreteModel()
m.time = ContinuousSet(initialize=[0,1])
m.x = pyo.Var(m.time, initialize=0)
m.y = pyo.Param(m.time, mutable=True, initialize=0)

discretizer = pyo.TransformationFactory("dae.finite_difference")
discretizer.apply_to(m, nfe=4, wrt=m.time, scheme="BACKWARD")

print(f"x[0.25] = {m.x[0.25].value}")
print(f"y[0.25] = {m.y[0.25].value}")

Error Message

x[0.25] = 0
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[2], line 13
     10 discretizer.apply_to(m, nfe=4, wrt=m.time, scheme="BACKWARD")
     12 print(f"x[0.25] = {m.x[0.25].value}")
---> 13 print(f"y[0.25] = {m.y[0.25].value}")

File ~\miniforge3\envs\idaes-fresh\Lib\site-packages\pyomo\core\base\param.py:230, in ParamData.value(self)
    227 @property
    228 def value(self):
    229     """Return the value for this variable."""
--> 230     return self()

File ~\miniforge3\envs\idaes-fresh\Lib\site-packages\pyomo\core\base\param.py:217, in ParamData.__call__(self, exception)
    215 if self._value is Param.NoValue:
    216     if exception:
--> 217         raise ValueError(
    218             "Error evaluating Param value (%s):\n\tThe Param value is "
    219             "currently set to an invalid value.  This is\n\ttypically "
    220             "from a scalar Param or mutable Indexed Param without\n"
    221             "\tan initial or default value." % (self.name,)
    222         )
    223     else:
    224         return None

ValueError: Error evaluating Param value (y[0.25]):
        The Param value is currently set to an invalid value.  This is
        typically from a scalar Param or mutable Indexed Param without
        an initial or default value

Application and Workaround

As part of a larger IDAES model, I want a time-derivative term to exist regardless of whether the system is steady-state or dynamic. If it's steady-state, I want it to be a Param set to 0:

        if self.config.dynamic is True:
            self.dTdt = DerivativeVar(
                self.drum_wall_temperature, wrt=self.flowsheet().time
            )
        else:
            self.dTdt = Param(
                self.flowsheet().time,
                self.dimensionless_radial_domain,
                initialize=0,
                mutable=True
            )

A workaround is to use an Expression instead of a Param:

        if self.config.dynamic is True:
            self.dTdt = DerivativeVar(
                self.drum_wall_temperature, wrt=self.flowsheet().time
            )
        else:
            @self.Expression(self.flowsheet().time, self.dimensionless_radial_domain)
            def dTdt(b, t, r):
                return 0 

Information on your system

Pyomo version: 6.10.1
Python version: 3.13.14
Operating system: Windows 11
How Pyomo was installed (PyPI, conda, source): IDAES developer installation
Solver (if applicable): n/a

Additional information