fix(CVODE_solver_strategy): solved a bug wherein mass fractions were not being properly computed from molar abundances.

src/include/gridfire/utils/general_composition.h

@@ -3,7 +3,7 @@
 #include "fourdst/composition/atomicSpecies.h"
 
 namespace gridfire::utils {
-    inline double massFractionFromMolarAbundance (
+    inline double massFractionFromMolarAbundanceAndComposition (
         const fourdst::composition::Composition& composition,
         const fourdst::atomic::Species& species,
         const double Yi
@@ -18,4 +18,58 @@ namespace gridfire::utils {
         }
         return (species.mass() * Yi) / sum;
     };
+
+    /**
+     * @brief Convert a vector of molar abundances into a vector of mass fractions
+     * @param molarAbundances Vector of molar abundances
+     * @param molarMasses Vector of molar masses
+     *
+     * @note The vectors molarAbundances and molarMasses must be parallel. This function does not provide any checks
+     * to ensure that the correct molar mass is being used with the correct molar abundance.
+     * @return A vector of molar masses such that each molar mass < 1 and the sum of all is = 1
+     */
+    inline std::vector<double> massFractionFromMolarAbundanceAndMolarMass (
+        const std::vector<double>& molarAbundances,
+        const std::vector<double>& molarMasses
+    ) noexcept {
+        assert(molarMasses.size() == molarAbundances.size());
+        assert(!molarMasses.empty());
+
+        double totalMass = 0;
+        std::vector<double> masses;
+        masses.reserve(molarMasses.size());
+        for (const auto [m, Y] : std::views::zip(molarMasses, molarAbundances)) {
+            const double mass = m * Y;
+            totalMass += mass;
+            masses.push_back(mass);
+        }
+
+        assert(totalMass > 0);
+
+        std::vector<double> massFractions;
+        massFractions.reserve(masses.size());
+        std::ranges::transform(
+            masses,
+            std::back_inserter(massFractions),
+            [&totalMass](const double speciesMass) {
+                const double Xi = speciesMass / totalMass;
+                if (std::abs(Xi) < 1e-16 && Xi < 0) {
+                    return 0.0;
+                }
+                return Xi;
+            });
+
+        return massFractions;
+    }
+
+    inline std::vector<double> molarMassVectorFromComposition(
+        const fourdst::composition::Composition& composition
+    ) {
+        std::vector<double> molarMassVector;
+        molarMassVector.reserve(composition.getRegisteredSymbols().size());
+        for (const auto &entry: composition | std::views::values) {
+            molarMassVector.push_back(entry.isotope().mass());
+        }
+        return molarMassVector;
+    }
 }