OdeSolver.hpp File Reference

Runge-Kutta-Cash-Karp (RK45) ODE integrator with adaptive step control. More...

#include <functional>
#include <vector>

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Namespaces
namespace	openswmm
namespace	openswmm::ode

Typedefs
using	openswmm::ode::DerivFunc = std::function< void(double x, const double *y, double *dydx)>
	Derivative function signature.
using	openswmm::ode::BatchDerivFunc = std::function< void(double x, const double *y0, const double *y1, double *dy0, double *dy1, int n_sys)>
	Integrate N independent 2-equation ODE systems in batch.

Functions
int	openswmm::ode::integrate (double *y, int n, double x1, double x2, double eps, double h1, const DerivFunc &derivs)
	Integrate an ODE system from x1 to x2 using RK45 Cash-Karp.
int	openswmm::ode::integrate_batch_2eq (double *y0, double *y1, int n_sys, double x1, double x2, double eps, double h1, const BatchDerivFunc &derivs)

Variables
constexpr int	openswmm::ode::MAXSTP = 10000
	Maximum integration steps.
constexpr double	openswmm::ode::TINY = 1.0e-30
	Underflow protection.
constexpr double	openswmm::ode::SAFETY = 0.9
	Step adjustment safety factor.
constexpr double	openswmm::ode::PGROW = -0.2
	Exponent for step increase.
constexpr double	openswmm::ode::PSHRNK = -0.25
	Exponent for step decrease.
constexpr double	openswmm::ode::ERRCON = 1.89e-4
	= (5/SAFETY)^(1/PGROW)
constexpr int	openswmm::ode::ODE_OK = 0
	Success.
constexpr int	openswmm::ode::ODE_TOO_MANY = 1
	n > allocated max
constexpr int	openswmm::ode::ODE_UNDERFLOW = 2
	Step size underflowed.
constexpr int	openswmm::ode::ODE_MAX_STEPS = 3
	Exceeded MAXSTP.

Detailed Description

Runge-Kutta-Cash-Karp (RK45) ODE integrator with adaptive step control.

Numerically identical to legacy odesolve.c. Uses 5th-order Runge-Kutta with embedded 4th-order error estimate for automatic step size control.

Used by:

• Groundwater two-zone model (2 ODEs per subcatchment)
• Subcatchment runoff ponded-depth integration

Vectorization note: Each subcatchment's ODE system is independent. For batch integration over N subcatchments, call integrate() N times or use integrate_batch() which processes all subcatchments in a single pass with SoA state arrays.

Note

Legacy reference: src/legacy/engine/odesolve.c

Author

Caleb Buahin caleb.nosp@m..bua.nosp@m.hin@g.nosp@m.mail.nosp@m..com

Copyright

Copyright (c) 2026 HydroCouple. All rights reserved.

License\n MIT License