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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-631) "RegulaFalsiSolver" failure
Date Sun, 07 Aug 2011 23:08:27 GMT

    [ https://issues.apache.org/jira/browse/MATH-631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13080690#comment-13080690
] 

Gilles commented on MATH-631:
-----------------------------

[My comment starting with "I understand what you say." was an answer to Luc. I hadn't read
Phil's previous one which was posted while I was writing mine.]

I agree that it is better not to change the standard algorithm, as I indicated in my first
comment.
The fix which I'm proposing is not an algorithm change, it is an implementation detail similar
to the many hundreds checks performed in CM. Just it is not a precondition test. It adequately
indicates that something went wrong and can help the user figure out what it was. It makes
the implementation more robust.


> "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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