## org.apache.commons.math3.analysis.solvers Class RegulaFalsiSolver

```java.lang.Object
org.apache.commons.math3.analysis.solvers.BaseAbstractUnivariateSolver<UnivariateFunction>
org.apache.commons.math3.analysis.solvers.AbstractUnivariateSolver
org.apache.commons.math3.analysis.solvers.BaseSecantSolver
org.apache.commons.math3.analysis.solvers.RegulaFalsiSolver
```
All Implemented Interfaces:
BaseUnivariateSolver<UnivariateFunction>, BracketedUnivariateSolver<UnivariateFunction>, UnivariateSolver

`public class RegulaFalsiSolverextends BaseSecantSolver`

Implements the Regula Falsi or False position method for root-finding (approximating a zero of a univariate real function). It is a modified `Secant` method.

The Regula Falsi method is included for completeness, for testing purposes, for educational purposes, for comparison to other algorithms, etc. It is however not intended to be used for actual problems, as one of the bounds often remains fixed, resulting in very slow convergence. Instead, one of the well-known modified Regula Falsi algorithms can be used (`Illinois` or `Pegasus`). These two algorithms solve the fundamental issues of the original Regula Falsi algorithm, and greatly out-performs it for most, if not all, (practical) functions.

Unlike the Secant method, the Regula Falsi guarantees convergence, by maintaining a bracketed solution. Note however, that due to the finite/limited precision of Java's `double` type, which is used in this implementation, the algorithm may get stuck in a situation where it no longer makes any progress. Such cases are detected and result in a `ConvergenceException` exception being thrown. In other words, the algorithm theoretically guarantees convergence, but the implementation does not.

The Regula Falsi method assumes that the function is continuous, but not necessarily smooth.

Implementation based on the following article: M. Dowell and P. Jarratt, A modified regula falsi method for computing the root of an equation, BIT Numerical Mathematics, volume 11, number 2, pages 168-174, Springer, 1971.

Since:
3.0
Version:
\$Id: RegulaFalsiSolver.java 1364387 2012-07-22 18:14:11Z tn \$

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.commons.math3.analysis.solvers.BaseSecantSolver
`BaseSecantSolver.Method`

Field Summary

Fields inherited from class org.apache.commons.math3.analysis.solvers.BaseSecantSolver
`DEFAULT_ABSOLUTE_ACCURACY`

Constructor Summary
`RegulaFalsiSolver()`
Construct a solver with default accuracy (1e-6).
`RegulaFalsiSolver(double absoluteAccuracy)`
Construct a solver.
```RegulaFalsiSolver(double relativeAccuracy, double absoluteAccuracy)```
Construct a solver.
```RegulaFalsiSolver(double relativeAccuracy, double absoluteAccuracy, double functionValueAccuracy)```
Construct a solver.

Method Summary

Methods inherited from class org.apache.commons.math3.analysis.solvers.BaseSecantSolver
`doSolve, solve, solve, solve`

Methods inherited from class org.apache.commons.math3.analysis.solvers.BaseAbstractUnivariateSolver
`computeObjectiveValue, getAbsoluteAccuracy, getEvaluations, getFunctionValueAccuracy, getMax, getMaxEvaluations, getMin, getRelativeAccuracy, getStartValue, incrementEvaluationCount, isBracketing, isSequence, setup, solve, solve, verifyBracketing, verifyInterval, verifySequence`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Methods inherited from interface org.apache.commons.math3.analysis.solvers.BaseUnivariateSolver
`getAbsoluteAccuracy, getEvaluations, getFunctionValueAccuracy, getMaxEvaluations, getRelativeAccuracy, solve, solve`

Constructor Detail

### RegulaFalsiSolver

`public RegulaFalsiSolver()`
Construct a solver with default accuracy (1e-6).

### RegulaFalsiSolver

`public RegulaFalsiSolver(double absoluteAccuracy)`
Construct a solver.

Parameters:
`absoluteAccuracy` - Absolute accuracy.

### RegulaFalsiSolver

```public RegulaFalsiSolver(double relativeAccuracy,
double absoluteAccuracy)```
Construct a solver.

Parameters:
`relativeAccuracy` - Relative accuracy.
`absoluteAccuracy` - Absolute accuracy.

### RegulaFalsiSolver

```public RegulaFalsiSolver(double relativeAccuracy,
double absoluteAccuracy,
double functionValueAccuracy)```
Construct a solver.

Parameters:
`relativeAccuracy` - Relative accuracy.
`absoluteAccuracy` - Absolute accuracy.
`functionValueAccuracy` - Maximum function value error.