[thermo] initial exposing of Peng-Robinson eos parameters to python interface

include/cantera/thermo/PengRobinson.h

@@ -173,6 +173,14 @@ public:
     void setBinaryCoeffs(const string& species_i, const string& species_j, double a);
     //! @}
 
+    //! Compute additional method based on name
+    /*!
+     * @param name The name of the quantity to compute
+     * @return Computed value wrapped in AnyValue type for Peng-Robinson phase
+     *         quantities
+     */
+    AnyValue compute_extra_method(const std::string& name) override;
+
 protected:
     // Special functions inherited from MixtureFugacityTP
     double sresid() const override;

include/cantera/thermo/ThermoPhase.h

@@ -1556,6 +1556,16 @@ public:
             const Composition& oxComp, ThermoBasis basis=ThermoBasis::molar) const;
     //! @}
 
+    //! Compute additional method based on name
+    /*!
+     * @param name The name of the quantity to compute
+     * @return Computed value wrapped in AnyValue type
+     */
+    virtual AnyValue compute_extra_method(const std::string& name)
+    {
+        throw NotImplementedError("ThermoPhase::compute_extra_method");
+    }
+
 private:
 
     //! Carry out work in HP and UV calculations.

interfaces/cython/cantera/thermo.pxd

@@ -175,6 +175,8 @@ cdef extern from "cantera/thermo/ThermoPhase.h" namespace "Cantera":
         double equivalenceRatio() except +translate_exception
         double stoichAirFuelRatio(const double* fuelComp, const double* oxComp, ThermoBasis basis) except +translate_exception
 
+        CxxAnyValue compute_extra_method(string) except +translate_exception
+
 
 cdef extern from "cantera/thermo/SurfPhase.h":
     cdef cppclass CxxSurfPhase "Cantera::SurfPhase":

interfaces/cython/cantera/thermo.pyx

@@ -1172,6 +1172,10 @@ cdef class ThermoPhase(_SolutionBase):
         X = self.thermo.getMoleFractionsByName(threshold)
         return {pystr(item.first):item.second for item in X}
 
+    def compute_extra_method(self, name):
+        cdef CxxAnyValue value = self.thermo.compute_extra_method(stringify(name))
+        return anyvalue_to_python(name, value)
+
     ######## Read-only thermodynamic properties ########
 
     property P:

src/thermo/PengRobinson.cpp

@@ -780,4 +780,18 @@ int PengRobinson::solveCubic(double T, double pres, double a, double b, double a
                                          an, bn, cn, dn, tc, vc);
 }
 
+AnyValue PengRobinson::compute_extra_method(const std::string& name)
+{
+    if(name == "aAlpha_mix") {
+        return AnyValue(m_aAlpha_mix);
+    } else if(name == "b_mix") {
+        return AnyValue(m_b);
+    } else if(name == "daAlpha_dT") {
+        return AnyValue(daAlpha_dT());
+    } else if(name == "d2aAlpha_dT2") {
+        return AnyValue(d2aAlpha_dT2());
+    }
+    throw CanteraError("PengRobinson::compute_extra_method", "Unknown method: {}", name);
+}
+
 }