findroot.c File Reference

Numerical root finding used by legacy hydraulic calculations. More...

#include <math.h>
#include "findroot.h"

Include dependency graph for findroot.c:

Macros
#define	SIGN(a, b)
#define	MAXIT   60

Functions
int	findroot_Newton (double x1, double x2, double *rts, double xacc, newton_callback func, void *p)
	Find a bracketed root using Newton steps with bisection fallback.
double	findroot_Ridder (double x1, double x2, double xacc, ridder_callback func, void *p)
	Estimate a bracketed scalar root with derivative-free Ridder iterations.

Detailed Description

Numerical root finding used by legacy hydraulic calculations.

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.

Macro Definition Documentation

MAXIT

#define MAXIT   60

SIGN

#define SIGN	(		a,
			b )

Value:

((b) >= 0.0 ? fabs(a) : -fabs(a))

Function Documentation

findroot_Newton()

int findroot_Newton	(	double	x1,
		double	x2,
		double *	rts,
		double	xacc,
		newton_callback	func,
		void *	p )

Find a bracketed root using Newton steps with bisection fallback.

Finds the root of a function using Newton's method.

Implementation arguments

• x1 (in): Bracket endpoint where the callback function is negative.
• x2 (in): Bracket endpoint where the callback function is positive; coordinate order may be reversed to obtain this sign ordering.
• rts (in,out): Non-null initial guess within the bracket, overwritten with the last estimate on convergence or iteration exhaustion.
• xacc (in): Positive absolute step tolerance in the coordinate units.
• func (in): Non-null synchronous callback filling f and df/dx; it must not retain the solver's temporary output pointers.
• p (in): Borrowed opaque callback context, passed through unchanged; may be NULL when the callback does not require it.

Returns

Evaluation count, or zero after more than MAXIT evaluations. A stationary floating-point estimate also ends iteration.

Precondition

The caller validates/orients the bracket. Endpoints are not evaluated before the initial guess, preserving the legacy callback sequence.

findroot_Ridder()

double findroot_Ridder	(	double	x1,
		double	x2,
		double	xacc,
		ridder_callback	func,
		void *	p )

Estimate a bracketed scalar root with derivative-free Ridder iterations.

Finds the root of a function using Ridder's method.

Implementation arguments

• x1 (in): First bracket coordinate.
• x2 (in): Second bracket coordinate; endpoint function values must have opposite signs unless an endpoint is already a root.
• xacc (in): Positive absolute tolerance in the coordinate units.
• func (in): Non-null synchronous evaluator; called at both endpoints and successive trial points, without retaining the callback.
• p (in): Borrowed opaque callback context; may be NULL if unused.

Returns

Exact endpoint root, the last approximate root, or -1.0e20 for an unbracketed root. Exhaustion has no separate failure status.

Note

When a newly calculated root is within xacc of the previous estimate, the previous estimate is returned; the last callback point may differ.