Adaptive integration of ordinary differential equations. More...

This graph shows which files directly or indirectly include this file:

Functions
int	odesolve_open (int n)
	Allocate the legacy solver's shared workspace for n equations.

void	odesolve_close (void)
	Free every legacy ODE workspace array and reset capacity to zero.

int	odesolve_integrate (double ystart[], int n, double x1, double x2, double eps, double h1, void(derivs)(double, double , double *))
	Integrate an ODE system with adaptive Cash-Karp RK45 steps.

Detailed Description

Adaptive integration of ordinary differential equations.

Author: Caleb Buahin caleb.nosp@m..bua.nosp@m.hin@g.nosp@m.mail.nosp@m..com (OpenSWMM maintenance and extensions)

Copyright: Copyright (c) 2026 Caleb Buahin. OpenSWMM contributions only; original EPA SWMM credits are retained.

License: Apache-2.0 for OpenSWMM contributions; original EPA SWMM provenance is retained.

Function Documentation

void odesolve_close ( void )

Free every legacy ODE workspace array and reset capacity to zero.

Note: Safe after partial allocation or a previous close; pointers are reset to NULL. Must not run concurrently with integration or inside its callback.

Here is the caller graph for this function:

Integrate an ODE system with adaptive Cash-Karp RK45 steps.

Parameters

[in,out]	ystart	Non-null array of n initial states at x1, replaced with states at x2 on success; unchanged on an error return.
[in]	n	Positive equation count, no larger than allocated nmax.
[in]	x1	Finite start coordinate in caller-selected units.
[in]	x2	Finite end coordinate in the same units.
[in]	eps	Positive dimensionless tolerance relative to each state scale abs(y) + abs(h * dydx) + TINY.
[in]	h1	Nonzero initial step, in x units, directed from x1 toward x2.
[in]	derivs	Non-null synchronous callback filling n dy/dx values from n states; borrowed arrays must not be modified or retained except for writing the derivative output.

Returns: Zero on success, one when n exceeds nmax, two for a zero next step, or three for exhausted iterations or underflow during rejection.

Precondition: odesolve_open() succeeded. The callback must not recursively integrate because accepted states and intermediate buffers are shared globals.

Here is the call graph for this function:

Here is the caller graph for this function:

int odesolve_open ( int n )

Allocate the legacy solver's shared workspace for n equations.

Parameters

[in] n Positive equation capacity; n * 5 must be representable as int.

Returns: One after all allocations succeed, zero when an allocation returns NULL.

Postcondition: Sets nmax only after success; partial allocations remain for odesolve_close(). Arrays are zero-initialized and shared across all calls.

Precondition: Any earlier workspace has been closed. Calling open twice without close overwrites owned pointers. The legacy solver is not thread-safe.

Here is the caller graph for this function: