docs(docs): asdded and cleaned up docs

src/include/gridfire/partition/partition_ground.h

@@ -10,33 +10,99 @@
 #include "quill/Logger.h"
 
 namespace gridfire::partition {
-    class GroundStatePartitionFunction final : public PartitionFunction {
-    public:
-        GroundStatePartitionFunction();
-        double evaluate(
-            const int z,
-            const int a,
-            const double T9
-        ) const override;
-        double evaluateDerivative(
-            const int z,
-            const int a,
-            const double T9
-        ) const override;
-        bool supports(
-            const int z,
-            const int a
-        ) const override;
-        std::string type() const override { return "GroundState"; }
-        std::unique_ptr<PartitionFunction> clone() const override {
-            return std::make_unique<GroundStatePartitionFunction>(*this);
-        }
-    private:
-        quill::Logger* m_logger = fourdst::logging::LogManager::getInstance().getLogger("log");
-        std::unordered_map<int, double> m_ground_state_spin;
-        static constexpr int make_key(
-            const int z,
-        const int a);
-    };
+    /**
+     * @class GroundStatePartitionFunction
+     * @brief Partition function implementation for nuclear ground states.
+     *
+     * Computes the partition function as (2J + 1) based on the ground state spin J of each isotope.
+     * The temperature derivative is always zero. Ground state spins are loaded from the
+     * fourdst::atomic::species registry at construction.
+     * @see partition_ground.cpp for implementation details.
+     */
+     class GroundStatePartitionFunction final : public PartitionFunction {
+     public:
+        /**
+         * @brief Construct and populate the ground state spin map.
++         *
+         * Loads spins for all isotopes from the atomic species registry into m_ground_state_spin.
+         * @pre atomic::species registry is initialized and non-empty.
+         * @post m_ground_state_spin contains entries for each isotope.
++         */
+         GroundStatePartitionFunction();
+        /**
+         * @brief Evaluate the ground state partition function.
++         *
+         * @param z Proton number (atomic number) of the isotope; must be >= 1.
+         * @param a Mass number of the isotope; must be >= z.
+         * @param T9 Temperature in units of 10^9 K; unused for ground state.
+         * @pre supports(z,a) returns true.
+         * @post No side effects.
+         * @return Dimensionless partition function value = 2*spin + 1.
+         * @throws std::out_of_range If the isotope key is not found in m_ground_state_spin.
++         */
+         double evaluate(
+             const int z,
+             const int a,
+             const double T9
+         ) const override;
+        /**
+         * @brief Evaluate the temperature derivative of the ground state partition function.
++         *
+         * Always returns zero as ground state has no temperature dependence.
+         * @param z Proton number of the isotope; must be supported.
+         * @param a Mass number of the isotope; must be supported.
+         * @param T9 Temperature in units of 10^9 K; unused.
+         * @pre supports(z,a) returns true.
+         * @post No side effects.
+         * @return Zero.
+         * @throws std::out_of_range If the isotope key is not found.
++         */
+         double evaluateDerivative(
+             const int z,
+             const int a,
+             const double T9
+         ) const override;
+        /**
+         * @brief Check if ground state data exists for the given isotope.
++         *
+         * @param z Proton number of the isotope.
+         * @param a Mass number of the isotope.
+         * @return True if m_ground_state_spin contains the key; false otherwise.
+         * @post No side effects.
++         */
+         bool supports(
+             const int z,
+             const int a
+         ) const override;
+        /**
+         * @brief Get the type identifier of this partition function.
+         * @return The string literal "GroundState".
+         * @post No side effects.
++         */
+         std::string type() const override { return "GroundState"; }
+        /**
+         * @brief Create a deep copy of this partition function.
+         * @return Unique_ptr to a new GroundStatePartitionFunction cloned from this object.
+         * @post Caller owns the returned instance.
++         */
+         std::unique_ptr<PartitionFunction> clone() const override {
+             return std::make_unique<GroundStatePartitionFunction>(*this);
+         }
+     private:
+         quill::Logger* m_logger = fourdst::logging::LogManager::getInstance().getLogger("log");
+         std::unordered_map<int, double> m_ground_state_spin;
+        /**
+         * @brief Generate a unique lookup key for an isotope.
++         *
+         * Combines atomic number z and mass number a into a single integer.
+         * @param z Proton number of the isotope.
+         * @param a Mass number of the isotope; should be < 1000 to avoid collisions.
+         * @pre a < 1000.
+         * @return Integer key = z * 1000 + a.
++         */
+         static constexpr int make_key(
+             const int z,
+         const int a);
+     };
 
-}
+ }