IntegratorTypes.hpp

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#pragma once

 
#include <algorithm>
#include <cctype>
#include <icarus/core/CoreTypes.hpp>
#include <stdexcept>
#include <string>
 
namespace icarus {
 
// =============================================================================
// Integrator Type Enumeration
// =============================================================================

enum class IntegratorType {
    Euler, 
    RK2,   
    RK4,   
    RK45   
};

[[nodiscard]] inline std::string to_string(IntegratorType type) {
    switch (type) {
    case IntegratorType::Euler:
        return "Euler";
    case IntegratorType::RK2:
        return "RK2";
    case IntegratorType::RK4:
        return "RK4";
    case IntegratorType::RK45:
        return "RK45";
    }
    return "Unknown";
}

[[nodiscard]] inline IntegratorType parse_integrator_type(const std::string &name) {
    std::string lower = name;
    std::transform(lower.begin(), lower.end(), lower.begin(),
                   [](unsigned char c) { return std::tolower(c); });
 
    if (lower == "euler")
        return IntegratorType::Euler;
    if (lower == "rk2")
        return IntegratorType::RK2;
    if (lower == "rk4")
        return IntegratorType::RK4;
    if (lower == "rk45")
        return IntegratorType::RK45;
    throw std::invalid_argument("Unknown integrator type: " + name);
}
 
// =============================================================================
// Integrator Configuration
// =============================================================================

template <typename Scalar> struct IntegratorConfig {
    IntegratorType type = IntegratorType::RK4; 
 
    // Adaptive stepping parameters (RK45 only)
    Scalar abs_tol = Scalar{1e-6};      
    Scalar rel_tol = Scalar{1e-6};      
    Scalar min_dt = Scalar{1e-10};      
    Scalar max_dt = Scalar{1.0};        
    Scalar safety_factor = Scalar{0.9}; 

    static IntegratorConfig RK4Default() {
        IntegratorConfig cfg;
        cfg.type = IntegratorType::RK4;
        return cfg;
    }

    static IntegratorConfig RK45Adaptive(Scalar abs_tol_val = Scalar{1e-6},
                                         Scalar rel_tol_val = Scalar{1e-6}) {
        IntegratorConfig cfg;
        cfg.type = IntegratorType::RK45;
        cfg.abs_tol = abs_tol_val;
        cfg.rel_tol = rel_tol_val;
        return cfg;
    }

    static IntegratorConfig ForMethod(IntegratorType method) {
        IntegratorConfig cfg;
        cfg.type = method;
        return cfg;
    }
};
 
} // namespace icarus