minor improvements

thermosteam/_multi_stream.py

@@ -253,7 +253,7 @@ def __init__(self,
         if vlle: self.vlle(T, P)
 
     @classmethod
-    def from_streams(cls, streams):
+    def from_streams(cls, streams, thermo=None):
         if not streams: raise ValueError('at least one stream must be passed')
         self = cls.__new__(cls)
         self._streams = streams_by_phase = {i.phase: i for i in streams}
@@ -264,7 +264,7 @@ def from_streams(cls, streams):
         self.characterization_factors = {}
         self._thermal_condition = base._thermal_condition
         for i in others: i._thermal_condition = base._thermal_condition
-        self._load_thermo(base.thermo)
+        self._load_thermo(thermo or base.thermo)
         self.price = 0
         self._imol = MolarFlowIndexer.from_data(
             [streams_by_phase[i]._imol.data for i in phases], phases, 

thermosteam/_stream.py

@@ -29,6 +29,8 @@
     import biosteam as bst
 # from .constants import g
 
+MaterialIndexer = tmo.indexer.MaterialIndexer
+
 __all__ = ('Stream',)
 
 # %% Utilities
@@ -1632,7 +1634,7 @@ def copy_like(self, other):
         flow (kg/hr): Water  2
 
         """
-        if isinstance(other, tmo.MultiStream):
+        if isinstance(other.imol, MaterialIndexer):
             phases = other.phases
             if len(phases) == 1:
                 phase, = phases

thermosteam/equilibrium/dew_point.py

@@ -33,7 +33,7 @@ def x_iter(x, x_gamma, T, P, f_gamma, gamma_args):
     except: 
         return x
     if (x < 0).any():
-        raise Exception('liquid phase composition is infeasible')
+        return x
     mask = x > 1e3
     if mask.any():
         x[mask] = 1e3 +  np.log(x[mask] / 1e3) # Avoid crazy numbers