feat(precomputation): added precomputation

preformance speed up by a factor of ~5

src/network/include/gridfire/engine/engine_graph.h

@@ -63,6 +63,7 @@ namespace gridfire {
      */
     static constexpr double MIN_JACOBIAN_THRESHOLD = 1e-24;
 
+
     /**
      * @class GraphEngine
      * @brief A reaction network engine that uses a graph-based representation.
@@ -108,7 +109,7 @@ namespace gridfire {
          * This constructor uses the given set of reactions to construct the
          * reaction network.
          */
-        explicit GraphEngine(reaction::LogicalReactionSet reactions);
+        explicit GraphEngine(const reaction::LogicalReactionSet &reactions);
 
         /**
          * @brief Calculates the right-hand side (dY/dt) and energy generation rate.
@@ -302,8 +303,32 @@ namespace gridfire {
 
         [[nodiscard]] screening::ScreeningType getScreeningModel() const override;
 
+        void setPrecomputation(bool precompute);
+
+        [[nodiscard]] bool isPrecomputationEnabled() const;
 
     private:
+        struct PrecomputedReaction {
+            size_t reaction_index;
+            std::vector<size_t> unique_reactant_indices;
+            std::vector<int> reactant_powers;
+            double symmetry_factor;
+            std::vector<size_t> affected_species_indices;
+            std::vector<int> stoichiometric_coefficients;
+        };
+
+        struct constants {
+            const double u = Constants::getInstance().get("u").value; ///< Atomic mass unit in g.
+            const double Na = Constants::getInstance().get("N_a").value; ///< Avogadro's number.
+            const double c = Constants::getInstance().get("c").value; ///< Speed of light in cm/s.
+        };
+
+    private:
+        Config& m_config = Config::getInstance();
+        quill::Logger* m_logger = LogManager::getInstance().getLogger("log");
+
+        constants m_constants;
+
         reaction::LogicalReactionSet m_reactions; ///< Set of REACLIB reactions in the network.
         std::unordered_map<std::string_view, reaction::Reaction*> m_reactionIDMap; ///< Map from reaction ID to REACLIBReaction. //PERF: This makes copies of REACLIBReaction and could be a performance bottleneck.
 
@@ -319,9 +344,9 @@ namespace gridfire {
         screening::ScreeningType m_screeningType = screening::ScreeningType::BARE; ///< Screening type for the reaction network. Default to no screening.
         std::unique_ptr<screening::ScreeningModel> m_screeningModel = screening::selectScreeningModel(m_screeningType);
 
-        Config& m_config = Config::getInstance();
+        bool m_usePrecomputation = true; ///< Flag to enable or disable using precomputed reactions for efficiency. Mathematically, this should not change the results. Generally end users should not need to change this.
-        Constants& m_constants = Constants::getInstance(); ///< Access to physical constants.
+
-        quill::Logger* m_logger = LogManager::getInstance().getLogger("log");
+        std::vector<PrecomputedReaction> m_precomputedReactions; ///< Precomputed reactions for efficiency.
 
     private:
         /**
@@ -377,6 +402,8 @@ namespace gridfire {
          */
         void recordADTape();
 
+        void precomputeNetwork();
+
         /**
          * @brief Validates mass and charge conservation across all reactions.
          *
@@ -405,6 +432,13 @@ namespace gridfire {
             double T9
         );
 
+        [[nodiscard]] StepDerivatives<double> calculateAllDerivativesUsingPrecomputation(
+            const std::vector<double> &Y_in,
+            const std::vector<double>& bare_rates,
+            double T9,
+            double rho
+        ) const;
+
         /**
          * @brief Calculates the molar reaction flow for a given reaction.
          *
@@ -522,9 +556,9 @@ namespace gridfire {
             Y[i] = CppAD::CondExpLt(Y[i], zero, zero, Y[i]); // Ensure no negative abundances
         }
 
-        const T u = static_cast<T>(m_constants.get("u").value); // Atomic mass unit in grams
+        const T u = static_cast<T>(m_constants.u); // Atomic mass unit in grams
-        const T N_A = static_cast<T>(m_constants.get("N_a").value); // Avogadro's number in mol^-1
+        const T N_A = static_cast<T>(m_constants.Na); // Avogadro's number in mol^-1
-        const T c = static_cast<T>(m_constants.get("c").value); // Speed of light in cm/s
+        const T c = static_cast<T>(m_constants.c); // Speed of light in cm/s
 
         // --- SINGLE LOOP OVER ALL REACTIONS ---
         for (size_t reactionIndex = 0; reactionIndex < m_reactions.size(); ++reactionIndex) {

src/network/lib/engine/engine_graph.cpp

@@ -28,11 +28,15 @@ namespace gridfire {
     ):
      m_reactions(build_reaclib_nuclear_network(composition, false)) {
         syncInternalMaps();
+        precomputeNetwork();
     }
 
-    GraphEngine::GraphEngine(reaction::LogicalReactionSet reactions) :
+    GraphEngine::GraphEngine(
-        m_reactions(std::move(reactions)) {
+        const reaction::LogicalReactionSet &reactions
+    ) :
+    m_reactions(reactions) {
         syncInternalMaps();
+        precomputeNetwork();
     }
 
     StepDerivatives<double> GraphEngine::calculateRHSAndEnergy(
@@ -40,8 +44,19 @@ namespace gridfire {
         const double T9,
         const double rho
     ) const {
+        if (m_usePrecomputation) {
+            std::vector<double> bare_rates;
+            bare_rates.reserve(m_reactions.size());
+            for (const auto& reaction: m_reactions) {
+                bare_rates.push_back(reaction.calculate_rate(T9));
+            }
+
+            // --- The public facing interface can always use the precomputed version since taping is done internally ---
+            return calculateAllDerivativesUsingPrecomputation(Y, bare_rates, T9, rho);
+        } else {
             return calculateAllDerivatives<double>(Y, T9, rho);
         }
+    }
 
 
     void GraphEngine::syncInternalMaps() {
@@ -200,11 +215,90 @@ namespace gridfire {
         // This allows for dynamic network modification while retaining caching for networks which are very similar.
         if (validationReactionSet != m_reactions) {
             LOG_DEBUG(m_logger, "Reaction set not cached. Rebuilding the reaction set for T9={} and culling={}.", T9, culling);
-            m_reactions = std::move(validationReactionSet);
+            m_reactions = validationReactionSet;
             syncInternalMaps(); // Re-sync internal maps after updating reactions. Note this will also retrace the AD tape.
         }
     }
 
+    StepDerivatives<double> GraphEngine::calculateAllDerivativesUsingPrecomputation(
+        const std::vector<double> &Y_in,
+        const std::vector<double> &bare_rates,
+        const double T9,
+        const double rho
+    ) const {
+        // --- Calculate screening factors ---
+        const std::vector<double> screeningFactors = m_screeningModel->calculateScreeningFactors(
+            m_reactions,
+            m_networkSpecies,
+            Y_in,
+            T9,
+            rho
+        );
+
+        // --- Optimized loop ---
+        std::vector<double> molarReactionFlows;
+        molarReactionFlows.reserve(m_precomputedReactions.size());
+
+        for (const auto& precomp : m_precomputedReactions) {
+            double abundanceProduct = 1.0;
+            bool below_threshold = false;
+            for (size_t i = 0; i < precomp.unique_reactant_indices.size(); ++i) {
+                const size_t reactantIndex = precomp.unique_reactant_indices[i];
+                const int power = precomp.reactant_powers[i];
+                const double abundance = Y_in[reactantIndex];
+                if (abundance < MIN_ABUNDANCE_THRESHOLD) {
+                    below_threshold = true;
+                    break;
+                }
+
+                abundanceProduct *= std::pow(Y_in[reactantIndex], power);
+            }
+            if (below_threshold) {
+                molarReactionFlows.push_back(0.0);
+                continue; // Skip this reaction if any reactant is below the abundance threshold
+            }
+
+            const double bare_rate = bare_rates[precomp.reaction_index];
+            const double screeningFactor = screeningFactors[precomp.reaction_index];
+            const size_t numReactants = m_reactions[precomp.reaction_index].reactants().size();
+
+            const double molarReactionFlow =
+                    screeningFactor *
+                    bare_rate *
+                    precomp.symmetry_factor *
+                    abundanceProduct *
+                    std::pow(rho, numReactants);
+
+            molarReactionFlows.push_back(molarReactionFlow);
+        }
+
+        // --- Assemble molar abundance derivatives ---
+        StepDerivatives<double> result;
+        result.dydt.assign(m_networkSpecies.size(), 0.0); // Initialize derivatives to zero
+        for (size_t j = 0; j < m_precomputedReactions.size(); ++j) {
+            const auto& precomp = m_precomputedReactions[j];
+            const double R_j = molarReactionFlows[j];
+
+            for (size_t i = 0; i < precomp.affected_species_indices.size(); ++i) {
+                const size_t speciesIndex = precomp.affected_species_indices[i];
+                const int stoichiometricCoefficient = precomp.stoichiometric_coefficients[i];
+
+                // Update the derivative for this species
+                result.dydt[speciesIndex] += static_cast<double>(stoichiometricCoefficient) * R_j / rho;
+            }
+        }
+
+        // --- Calculate the nuclear energy generation rate ---
+        double massProductionRate = 0.0; // [mol][s^-1]
+        for (size_t i = 0; i < m_networkSpecies.size(); ++i) {
+            const auto& species = m_networkSpecies[i];
+            massProductionRate += result.dydt[i] * species.mass() * m_constants.u;
+        }
+        result.nuclearEnergyGenerationRate = -massProductionRate * m_constants.Na * m_constants.c * m_constants.c; // [erg][s^-1][g^-1]
+        return result;
+
+    }
+
     // --- Generate Stoichiometry Matrix ---
     void GraphEngine::generateStoichiometryMatrix() {
         LOG_TRACE_L1(m_logger, "Generating stoichiometry matrix...");
@@ -272,6 +366,14 @@ namespace gridfire {
         return m_screeningType;
     }
 
+    void GraphEngine::setPrecomputation(const bool precompute) {
+        m_usePrecomputation = precompute;
+    }
+
+    bool GraphEngine::isPrecomputationEnabled() const {
+        return m_usePrecomputation;
+    }
+
     double GraphEngine::calculateMolarReactionFlow(
         const reaction::Reaction &reaction,
         const std::vector<double> &Y,
@@ -450,7 +552,7 @@ namespace gridfire {
     }
 
     void GraphEngine::update(const NetIn &netIn) {
-        return; // No-op for GraphEngine, as it does not support manually triggering updates.
+        // No-op for GraphEngine, as it does not support manually triggering updates.
     }
 
     void GraphEngine::recordADTape() {
@@ -471,7 +573,7 @@ namespace gridfire {
         //    Their numeric values are irrelevant except for in so far as they avoid numerical instabilities.
 
         // Distribute total mass fraction uniformly between species in the dummy variable space
-        const auto uniformMassFraction = static_cast<CppAD::AD<double>>(1.0 / numSpecies);
+        const auto uniformMassFraction = static_cast<CppAD::AD<double>>(1.0 / static_cast<double>(numSpecies));
         std::vector<CppAD::AD<double>> adInput(numADInputs, uniformMassFraction);
         adInput[numSpecies]     = 1.0; // Dummy T9
         adInput[numSpecies + 1] = 1.0; // Dummy rho
@@ -497,4 +599,53 @@ namespace gridfire {
         LOG_TRACE_L1(m_logger, "AD tape recorded successfully for the RHS calculation. Number of independent variables: {}.",
                  adInput.size());
     }
+
+    void GraphEngine::precomputeNetwork() {
+        LOG_TRACE_L1(m_logger, "Pre-computing constant components of GraphNetwork state...");
+
+        // --- Reverse map for fast species lookups ---
+        std::unordered_map<fourdst::atomic::Species, size_t> speciesIndexMap;
+        for (size_t i = 0; i < m_networkSpecies.size(); ++i) {
+            speciesIndexMap[m_networkSpecies[i]] = i;
+        }
+
+        m_precomputedReactions.clear();
+        m_precomputedReactions.reserve(m_reactions.size());
+
+        for (size_t i = 0; i < m_reactions.size(); ++i) {
+            const auto& reaction = m_reactions[i];
+            PrecomputedReaction precomp;
+            precomp.reaction_index = i;
+
+            // --- Precompute reactant information ---
+            // Count occurrences for each reactant to determine powers and symmetry
+            std::unordered_map<size_t, int> reactantCounts;
+            for (const auto& reactant: reaction.reactants()) {
+                size_t reactantIndex = speciesIndexMap.at(reactant);
+                reactantCounts[reactantIndex]++;
+            }
+
+            double symmetryDenominator = 1.0;
+            for (const auto& [index, count] : reactantCounts) {
+                precomp.unique_reactant_indices.push_back(index);
+                precomp.reactant_powers.push_back(count);
+
+                symmetryDenominator *= 1.0/std::tgamma(count + 1);
+            }
+
+            precomp.symmetry_factor = symmetryDenominator;
+
+            // --- Precompute stoichiometry information ---
+            const auto stoichiometryMap = reaction.stoichiometry();
+            precomp.affected_species_indices.reserve(stoichiometryMap.size());
+            precomp.stoichiometric_coefficients.reserve(stoichiometryMap.size());
+
+            for (const auto& [species, coeff] : stoichiometryMap) {
+                precomp.affected_species_indices.push_back(speciesIndexMap.at(species));
+                precomp.stoichiometric_coefficients.push_back(coeff);
+            }
+
+            m_precomputedReactions.push_back(std::move(precomp));
+        }
+    }
 }

tests/graphnet_sandbox/main.cpp

@@ -19,9 +19,23 @@
 #include "quill/Backend.h"
 #include "quill/Frontend.h"
 
+#include <chrono>
+#include <functional>
+
 // Keep a copy of the previous handler
 static std::terminate_handler g_previousHandler = nullptr;
 
+void measure_execution_time(const std::function<void()>& callback, const std::string& name)
+{
+    // variable names in camelCase
+    const auto startTime   = std::chrono::steady_clock::now();
+    callback();
+    const auto endTime     = std::chrono::steady_clock::now();
+    const auto duration    = std::chrono::duration_cast<std::chrono::nanoseconds>(endTime - startTime);
+    std::cout << "Execution time for " << name << ": "
+              << duration.count()/1e9 << " s\n";
+}
+
 void quill_terminate_handler()
 {
     // 1. Stop the Quill backend (flushes all sinks and joins thread)
@@ -65,21 +79,28 @@ int main() {
 
     NetOut netOut;
 
-    netIn.dt0 = 1e12;
+    // netIn.dt0 = 1e12;
     // approx8::Approx8Network approx8Network;
+    // measure_execution_time([&]() {
     //     netOut = approx8Network.evaluate(netIn);
+    // }, "Approx8 Network Initialization");
     // std::cout << "Approx8 Network H-1: " << netOut.composition.getMassFraction("H-1") << " in " << netOut.num_steps << " steps." << std::endl;
 
 
     netIn.dt0 = 1e-15;
 
     GraphEngine ReaclibEngine(composition);
+    ReaclibEngine.setPrecomputation(true);
     // AdaptiveEngineView adaptiveEngine(ReaclibEngine);
     io::SimpleReactionListFileParser parser{};
     FileDefinedEngineView approx8EngineView(ReaclibEngine, "approx8.net", parser);
     approx8EngineView.setScreeningModel(screening::ScreeningType::WEAK);
     solver::QSENetworkSolver solver(approx8EngineView);
-
     netOut = solver.evaluate(netIn);
-    std::cout << "QSE Graph Network H-1: " << netOut.composition.getMassFraction("H-1") << " in " << netOut.num_steps << " steps." << std::endl;
+
+    // measure_execution_time([&]() {
+    //     netOut = solver.evaluate(netIn);
+    // }, "Approx8 Network Evaluation (Precomputation)");
+    // ReaclibEngine.setPrecomputation(false);
+    // std::cout << "Precomputation H-1: " << netOut.composition.getMassFraction("H-1") << " in " << netOut.num_steps << " steps." << std::endl;
 }