feat(partition-functions): added framework and some concrete partition functions

GroundState partition function, Rauscher&Thielemann partition function, and composite partition function added

src/network/lib/partition/partition_rauscher_thielemann.cpp

@@ -0,0 +1,141 @@
+#include "gridfire/partition/partition_rauscher_thielemann.h"
+#include "gridfire/partition/rauscher_thielemann_partition_data.h"
+#include "gridfire/partition/rauscher_thielemann_partition_data_record.h"
+
+#include "fourdst/logging/logging.h"
+#include "quill/LogMacros.h"
+
+#include <stdexcept>
+#include <algorithm>
+#include <vector>
+#include <array>
+
+namespace gridfire::partition {
+    static constexpr std::array<double, 24> RT_TEMPERATURE_GRID_T9 = {
+        0.01, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5,
+        2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0
+    };
+
+    RauscherThielemannPartitionFunction::RauscherThielemannPartitionFunction() {
+        constexpr size_t numRecords = rauscher_thielemann_partition_data_len / sizeof(record::RauscherThielemannPartitionDataRecord);
+        m_partitionData.reserve(numRecords);
+        const auto* records = reinterpret_cast<const record::RauscherThielemannPartitionDataRecord*>(rauscher_thielemann_partition_data);
+        for (size_t i = 0; i < numRecords; ++i) {
+            const auto& record = records[i];
+            IsotopeData data;
+            data.ground_state_spin = record.ground_state_spin;
+            std::ranges::copy(record.normalized_g_values, data.normalized_g_values.begin());
+
+            m_partitionData[make_key(record.z, record.a)] = std::move(data);
+        }
+    }
+
+    double RauscherThielemannPartitionFunction::evaluate(
+        const int z,
+        const int a,
+        const double T9
+    ) const {
+        LOG_TRACE_L2(m_logger, "Evaluating Rauscher-Thielemann partition function for Z={} A={} T9={}", z, a, T9);
+
+        const auto [bound, data, upperIndex, lowerIndex] = find(z, a, T9);
+
+        switch (bound) {
+            case FRONT: {
+                LOG_TRACE_L2(m_logger, "Using FRONT bound for Z={} A={} T9={}", z, a, T9);
+                return data.normalized_g_values.front() * (2.0 * data.ground_state_spin + 1.0);
+            }
+            case BACK: {
+                LOG_TRACE_L2(m_logger, "Using BACK bound for Z={} A={} T9={}", z, a, T9);
+                return data.normalized_g_values.back() * (2.0 * data.ground_state_spin + 1.0);
+            }
+            case MIDDLE: {
+                LOG_TRACE_L2(m_logger, "Using MIDDLE bound for Z={} A={} T9={}", z, a, T9);
+            }
+        }
+
+        const auto [T9_high, G_norm_high, T9_low, G_norm_low] = get_interpolation_points(
+            upperIndex,
+            lowerIndex,
+            data.normalized_g_values
+        );
+
+        const double frac = (T9 - T9_low) / (T9_high - T9_low);
+        const double interpolated_g_norm = G_norm_low + frac * (G_norm_high - G_norm_low);
+
+        return interpolated_g_norm * (2.0 * data.ground_state_spin + 1.0);
+    }
+
+    double RauscherThielemannPartitionFunction::evaluateDerivative(
+        const int z,
+        const int a,
+        const double T9
+    ) const {
+        LOG_TRACE_L2(m_logger, "Evaluating derivative of Rauscher-Thielemann partition function for Z={} A={} T9={}", z, a, T9);
+        const auto [bound, data, upperIndex, lowerIndex] = find(z, a, T9);
+        if (bound == FRONT || bound == BACK) {
+            LOG_TRACE_L2(m_logger, "Derivative is zero for Z={} A={} T9={} (bound: {})", z, a, T9, bound == FRONT ? "FRONT" : "BACK");
+            return 0.0; // Derivative is zero at the boundaries
+        }
+        const auto [T9_high, G_norm_high, T9_low, G_norm_low] = get_interpolation_points(
+            upperIndex,
+            lowerIndex,
+            data.normalized_g_values
+        );
+        const double slope_g_norm = (G_norm_high - G_norm_low) / (T9_high - T9_low);
+        return slope_g_norm * (2.0 * data.ground_state_spin + 1.0);
+    }
+
+    bool RauscherThielemannPartitionFunction::supports(
+        const int z,
+        const int a
+    ) const {
+        return m_partitionData.contains(make_key(z, a));
+    }
+
+    RauscherThielemannPartitionFunction::InterpolationPoints RauscherThielemannPartitionFunction::get_interpolation_points(
+        const size_t upper_index,
+        const size_t lower_index,
+        const std::array<double, 24>& normalized_g_values
+    ) {
+        const double T_high = RT_TEMPERATURE_GRID_T9[upper_index];
+        const double G_norm_high = normalized_g_values[upper_index];
+        const double T_low = RT_TEMPERATURE_GRID_T9[lower_index];
+        const double G_norm_low = normalized_g_values[lower_index];
+        return {T_high, G_norm_high, T_low, G_norm_low};
+    }
+
+    RauscherThielemannPartitionFunction::IdentifiedIsotope RauscherThielemannPartitionFunction::find(
+        const int z,
+        const int a,
+        const double T9
+    ) const {
+        const auto key = make_key(z, a);
+        const auto it = m_partitionData.find(key);
+
+        if (it == m_partitionData.end()) {
+            LOG_ERROR(m_logger, "Rauscher-Thielemann partition function data for Z={} A={} not found.", z, a);
+            throw std::out_of_range("Partition function data not found for Z=" + std::to_string(z) + " A=" + std::to_string(a));
+        }
+
+        const IsotopeData& data = it->second;
+        const auto upper_it = std::ranges::lower_bound(RT_TEMPERATURE_GRID_T9, T9);
+        Bounds bound;
+        if (upper_it == RT_TEMPERATURE_GRID_T9.begin()) {
+            bound = FRONT; // T9 is below the first grid point
+        } else if (upper_it == RT_TEMPERATURE_GRID_T9.end()) {
+            bound = BACK; // T9 is above the last grid point
+        } else {
+            bound = MIDDLE; // T9 is within the grid
+        }
+        const size_t upper_index = std::distance(RT_TEMPERATURE_GRID_T9.begin(), upper_it);
+        const size_t lower_index = upper_index - 1;
+        return {bound, data, upper_index, lower_index};
+    }
+
+    constexpr int RauscherThielemannPartitionFunction::make_key(
+        const int z,
+        const int a
+    ) {
+        return z * 1000 + a; // Simple key generation for Z and A
+    }
+}