[Python] Add Solution.state to allow faster iteration over states

interfaces/cython/cantera/_cantera.pxd

@@ -109,6 +109,8 @@ cdef extern from "cantera/thermo/ThermoPhase.h" namespace "Cantera":
         double refPressure() except +
         cbool getElementPotentials(double*) except +
         void equilibrate(string, string, double, int, int, int, int) except +
+        void saveState(size_t, double*)
+        void restoreState(size_t, double*)
 
         # initialization
         void addUndefinedElements() except +

interfaces/cython/cantera/composite.py

@@ -188,7 +188,7 @@ def setter(self, value):
     return property(getter, setter, doc=getattr(Solution, attr).__doc__)
 
 for _attr in dir(Solution):
-    if _attr.startswith('_') or _attr in Quantity.__dict__:
+    if _attr.startswith('_') or _attr in Quantity.__dict__ or _attr == 'state':
         continue
     else:
         setattr(Quantity, _attr, _prop(_attr))
@@ -205,37 +205,22 @@ def __init__(self, phase, shape, states=None):
         else:
             self._shape = shape
             S = np.empty(shape + (2+self._phase.n_species,))
-            S[...,0], S[...,1], S[...,2:] = self._phase.TDY
+            S[:] = self._phase.state
             self._states = S
 
         self._indices = list(np.ndindex(self._shape))
 
-    def __iter__(self):
-        """
-        Iterate over states, with the phase object set to the corresponding
-        state.
-        """
-        for index in self._indices:
-            state = self._states[index]
-            self._phase.TDY = state[0], state[1], state[2:]
-            yield index
-
-    def items(self):
-        for index in self._indices:
-            state = self._states[index]
-            self._phase.TDY = state[0], state[1], state[2:]
-            yield index, state
-
     def __getitem__(self, index):
         states = self._states[index]
         shape = states.shape[:-1]
         return SolutionArray(self._phase, shape, states)
 
     def equilibrate(self, *args, **kwargs):
         """ See `ThermoPhase.equilibrate` """
-        for index, state in self.items():
+        for index in self._indices:
+            self._phase.state = self._states[index]
             self._phase.equilibrate(*args, **kwargs)
-            state[0], state[1], state[2:] = self._phase.TDY
+            self._states[index][:] = self._phase.state
 
 
 def _make_functions():
@@ -270,16 +255,18 @@ def state2_prop(name):
         def getter(self):
             a = np.empty(self._shape)
             b = np.empty(self._shape)
-            for index in self:
+            for index in self._indices:
+                self._phase.state = self._states[index]
                 a[index], b[index] = getattr(self._phase, name)
             return a, b
 
         def setter(self, AB):
             assert len(AB) == 2, "Expected 2 elements, got {}".format(len(AB))
             A, B, _ = np.broadcast_arrays(AB[0], AB[1], self._states[...,0])
-            for index, state in self.items():
+            for index in self._indices:
+                self._phase.state = self._states[index]
                 setattr(self._phase, name, (A[index], B[index]))
-                state[0], state[1], state[2:] = self._phase.TDY
+                self._states[index][:] = self._phase.state
 
         return property(getter, setter, doc=getattr(Solution, name).__doc__)
 
@@ -293,17 +280,19 @@ def getter(self):
             a = np.empty(self._shape)
             b = np.empty(self._shape)
             c = np.empty(self._shape + (self._phase.n_species,))
-            for index in self:
+            for index in self._indices:
+                self._phase.state = self._states[index]
                 a[index], b[index], c[index] = getattr(self._phase, name)
             return a, b, c
 
         def setter(self, ABC):
             assert len(ABC) == 3, "Expected 3 elements, got {}".format(len(ABC))
             A, B, C, _ = np.broadcast_arrays(ABC[0], ABC[1], ABC[2],
                                              self._states[...,0])
-            for index, state in self.items():
+            for index in self._indices:
+                self._phase.state = self._states[index]
                 setattr(self._phase, name, (A[index], B[index], C[index]))
-                state[0], state[1], state[2:] = self._phase.TDY
+                self._states[index][:] = self._phase.state
 
         return property(getter, setter, doc=getattr(Solution, name).__doc__)
 
@@ -313,7 +302,8 @@ def setter(self, ABC):
     def scalar_prop(name):
         def getter(self):
             v = np.empty(self._shape)
-            for index in self:
+            for index in self._indices:
+                self._phase.state = self._states[index]
                 v[index] = getattr(self._phase, name)
             return v
         return property(getter, doc=getattr(Solution, name).__doc__)
@@ -324,7 +314,8 @@ def getter(self):
     def species_prop(name):
         def getter(self):
             v = np.empty(self._shape + (self._phase.n_species,))
-            for index in self:
+            for index in self._indices:
+                self._phase.state = self._states[index]
                 v[index] = getattr(self._phase, name)
             return v
         return property(getter, doc=getattr(Solution, name).__doc__)
@@ -336,7 +327,8 @@ def getter(self):
     def caller(name):
         def wrapper(self, *args, **kwargs):
             v = np.empty(self._shape)
-            for index in self:
+            for index in self._indices:
+                self._phase.state = self._states[index]
                 v[index] = getattr(self._phase, name)(*args, **kwargs)
             return v
         return wrapper

interfaces/cython/cantera/thermo.pyx

@@ -831,6 +831,22 @@ cdef class ThermoPhase(_SolutionBase):
 
     ######## Methods to get/set the complete thermodynamic state ########
 
+    property state:
+        """
+        Get/Set the full thermodynamic state as a single array, arranged as
+        [temperature, density, mass fractions] for most phases. Useful mainly
+        in cases where it is desired to store many states in a multidimensional
+        array.
+        """
+        def __get__(self):
+            cdef np.ndarray[np.double_t, ndim=1] state = np.empty(self.n_species + 2)
+            self.thermo.saveState(len(state), &state[0])
+            return state
+
+        def __set__(self, state):
+            cdef np.ndarray[np.double_t, ndim=1] cstate = np.asarray(state)
+            self.thermo.restoreState(len(state), &cstate[0])
+
     property TD:
         """Get/Set temperature [K] and density [kg/m^3 or kmol/m^3]."""
         def __get__(self):