[Python] Basic implementation of class Quantity

interfaces/cython/cantera/__init__.py

@@ -1,5 +1,6 @@
 from ._cantera import *
 from ._cantera import __version__, __sundials_version__
+from .composite import *
 from .liquidvapor import *
 from .onedim import *
 from .utils import *

interfaces/cython/cantera/composite.py

@@ -0,0 +1,104 @@
+from ._cantera import *
+
+class Quantity(object):
+    """
+    A class representing a specific quantity of a `Solution`.
+    """
+    def __init__(self, phase, mass=None, moles=None, constant='UV'):
+        self.state = phase.TDY
+        self._phase = phase
+
+        if mass is not None:
+            self.mass = mass
+        elif moles is not None:
+            self.moles = moles
+        else:
+            self.mass = 1.0
+
+        assert constant in ('TP','TV','HP','SP','SV','UV')
+        self.constant = constant
+
+    @property
+    def phase(self):
+        self._phase.TDY = self.state
+        return self._phase
+
+    @property
+    def moles(self):
+        return self.mass / self.phase.mean_molecular_weight
+
+    @moles.setter
+    def moles(self, n):
+        self.mass = n * self.phase.mean_molecular_weight
+
+    @property
+    def volume(self):
+        return self.mass * self.phase.volume_mass
+
+    @property
+    def int_energy(self):
+        return self.mass * self.phase.int_energy_mass
+
+    @property
+    def enthalpy(self):
+        return self.mass * self.phase.enthalpy_mass
+
+    @property
+    def entropy(self):
+        return self.mass * self.phase.entropy_mass
+
+    @property
+    def gibbs(self):
+        return self.mass * self.phase.gibbs_mass
+
+    def __imul__(self, other):
+        self.mass *= other
+        return self
+
+    def __mul__(self, other):
+        return Quantity(self.phase, mass=self.mass * other)
+
+    def __rmul__(self, other):
+        return Quantity(self.phase, mass=self.mass * other)
+
+    def __iadd__(self, other):
+        assert(self.constant == other.constant)
+        a1,b1 = getattr(self.phase, self.constant)
+        a2,b2 = getattr(other.phase, self.constant)
+        m = self.mass + other.mass
+        a = (a1 * self.mass + a2 * other.mass) / m
+        b = (b1 * self.mass + b2 * other.mass) / m
+        self._phase.Y = (self.Y * self.mass + other.Y * other.mass) / m
+        setattr(self._phase, self.constant, (a,b))
+        self.state = self._phase.TDY
+        self.mass = m
+        return self
+
+    def __add__(self, other):
+        newquantity = Quantity(self.phase, mass=self.mass, constant=self.constant)
+        newquantity += other
+        return newquantity
+
+# Synonyms for total properties
+Quantity.V = Quantity.volume
+Quantity.U = Quantity.int_energy
+Quantity.H = Quantity.enthalpy
+Quantity.S = Quantity.entropy
+Quantity.G = Quantity.gibbs
+
+# Add properties to act as pass-throughs for attributes of class Solution
+def _prop(attr):
+    def getter(self):
+        return getattr(self.phase, attr)
+
+    def setter(self, value):
+        setattr(self.phase, attr, value)
+        self.state = self._phase.TDY
+
+    return property(getter, setter, doc=getattr(Solution, attr).__doc__)
+
+for _attr in dir(Solution):
+    if _attr.startswith('_') or _attr in Quantity.__dict__:
+        continue
+    else:
+        setattr(Quantity, _attr, _prop(_attr))

interfaces/cython/cantera/test/test_thermo.py

@@ -910,3 +910,72 @@ def test_coeffs(self):
         self.assertEqual(st.max_temp, 3500)
         self.assertEqual(st.reference_pressure, 101325)
         self.assertArrayNear(self.h2o_coeffs, st.coeffs)
+
+
+class TestQuantity(utilities.CanteraTest):
+    @classmethod
+    def setUpClass(cls):
+        cls.gas = ct.Solution('gri30.xml')
+
+    def setUp(self):
+        self.gas.TPX = 300, 101325, 'O2:1.0, N2:3.76'
+
+    def test_mass_moles(self):
+        q1 = ct.Quantity(self.gas, mass=5)
+        self.assertNear(q1.mass, 5)
+        self.assertNear(q1.moles, 5 / q1.mean_molecular_weight)
+
+        q1.mass = 7
+        self.assertNear(q1.moles, 7 / q1.mean_molecular_weight)
+
+        q1.moles = 9
+        self.assertNear(q1.moles, 9)
+        self.assertNear(q1.mass, 9 * q1.mean_molecular_weight)
+
+    def test_extensive(self):
+        q1 = ct.Quantity(self.gas, mass=5)
+        self.assertNear(q1.mass, 5)
+
+        self.assertNear(q1.volume * q1.density, q1.mass)
+        self.assertNear(q1.V * q1.density, q1.mass)
+        self.assertNear(q1.int_energy, q1.moles * q1.int_energy_mole)
+        self.assertNear(q1.enthalpy, q1.moles * q1.enthalpy_mole)
+        self.assertNear(q1.entropy, q1.moles * q1.entropy_mole)
+        self.assertNear(q1.gibbs, q1.moles * q1.gibbs_mole)
+        self.assertNear(q1.int_energy, q1.U)
+        self.assertNear(q1.enthalpy, q1.H)
+        self.assertNear(q1.entropy, q1.S)
+        self.assertNear(q1.gibbs, q1.G)
+
+    def test_multiply(self):
+        q1 = ct.Quantity(self.gas, mass=5)
+        q2 = q1 * 2.5
+        self.assertNear(q1.mass * 2.5, q2.mass)
+        self.assertNear(q1.moles * 2.5, q2.moles)
+        self.assertNear(q1.entropy * 2.5, q2.entropy)
+        self.assertArrayNear(q1.X, q2.X)
+
+    def test_iadd(self):
+        q0 = ct.Quantity(self.gas, mass=5)
+        q1 = ct.Quantity(self.gas, mass=5)
+        q2 = ct.Quantity(self.gas, mass=5)
+        q2.TPX = 500, 101325, 'CH4:1.0'
+
+        q1 += q2
+        self.assertNear(q0.mass + q2.mass, q1.mass)
+        # addition is at constant UV
+        self.assertNear(q0.U + q2.U, q1.U)
+        self.assertNear(q0.V + q2.V, q1.V)
+        self.assertArrayNear(q0.X*q0.moles + q2.X*q2.moles, q1.X*q1.moles)
+
+    def test_add(self):
+        q1 = ct.Quantity(self.gas, mass=5)
+        q2 = ct.Quantity(self.gas, mass=5)
+        q2.TPX = 500, 101325, 'CH4:1.0'
+
+        q3 = q1 + q2
+        self.assertNear(q1.mass + q2.mass, q3.mass)
+        # addition is at constant UV
+        self.assertNear(q1.U + q2.U, q3.U)
+        self.assertNear(q1.V + q2.V, q3.V)
+        self.assertArrayNear(q1.X*q1.moles + q2.X*q2.moles, q3.X*q3.moles)