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https://issues.apache.org/jira/browse/MATH-631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13080478#comment-13080478
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Gilles commented on MATH-631:
-----------------------------
The problem was due to the fact that at some point, the update formula always
gave the same value: Nothing was being updated and the loop went on until the
number of evaluations was exhausted.
I've committed a tentative solution in revision 1154614.
However:
# I'm not sure that it doesn't have any adverse side-effects on the bracketing
property.
# It is quite probably not a pristine "regula falsi" algorithm anymore.
Please review.
Anyways, for the function that triggered the problem (see "testIssue631" in
"RegulaFalsiSolverTest.java"), the (modified) {{RegulaFalsiSolver}} takes 3624
evaluations (versus 17 for {{PegasusSolver}}). We should probably add a word of
warning in the class Javadoc.
> "RegulaFalsiSolver" failure
> ---------------------------
>
> Key: MATH-631
> URL: https://issues.apache.org/jira/browse/MATH-631
> Project: Commons Math
> Issue Type: Bug
> Reporter: Gilles
> Fix For: 3.0
>
>
> The following unit test:
> {code}
> @Test
> public void testBug() {
> final UnivariateRealFunction f = new UnivariateRealFunction() {
> @Override
> public double value(double x) {
> return Math.exp(x) - Math.pow(Math.PI, 3.0);
> }
> };
> UnivariateRealSolver solver = new RegulaFalsiSolver();
> double root = solver.solve(100, f, 1, 10);
> }
> {code}
> fails with
> {noformat}
> illegal state: maximal count (100) exceeded: evaluations
> {noformat}
> Using "PegasusSolver", the answer is found after 17 evaluations.
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