add decoupled phenomena features

thermosteam/_stream.py

@@ -25,7 +25,7 @@
 if TYPE_CHECKING:
     from .base import SparseVector, SparseArray
     from numpy.typing import NDArray
-    from typing import Optional, Sequence
+    from typing import Optional, Sequence, Callable
     import biosteam as bst
 # from .constants import g
 
@@ -260,7 +260,7 @@ class Stream:
         '_bubble_point_cache', '_dew_point_cache',
         '_vle_cache', '_lle_cache', '_sle_cache',
         '_sink', '_source', '_price', '_property_cache_key',
-        '_property_cache', 'characterization_factors',
+        '_property_cache', 'characterization_factors', 'equations',
         'port', # '_velocity', '_height'
     )
     line = 'Stream'
@@ -291,6 +291,7 @@ def __init__(self, ID: Optional[str]='',
                  vlle: Optional[bool]=False,
                  # velocity=0., height=0.,
                  **chemical_flows:float):
+        self.equations: dict[str, list[Callable]] = {} 
         #: Characterization factors for life cycle assessment [impact/kg].
         self.characterization_factors: dict[str, float] = {} if characterization_factors is None else {}
         self._thermal_condition = tmo.ThermalCondition(T, P)
@@ -354,6 +355,21 @@ def __getitem__(self, key):
     def __reduce__(self):
         return self.from_data, (self.get_data(), self._ID, self._price, self.characterization_factors, self._thermo)
 
+    def equation(self, variable, f=None):
+        if f is None: return lambda f: self.equation(variable, f)
+        equations = self.equations
+        if variable in equations:
+            equations[variable].append(f)
+        else:
+            equations[variable] = [f]
+
+    def _create_linear_equations(self, variable):
+        equations = self.equations
+        if variable in equations:
+            return [i() for i in equations[variable]]
+        else:
+            return []
+
     def _update_decoupled_variable(self, variable, value):
         if variable == 'mol': 
             self.mol[:] = value