[ https://issues.apache.org/jira/browse/MATH-700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13141103#comment-13141103 ] Gilles commented on MATH-700: ----------------------------- We could create a new "bracket" method with an additional boolean parameter to indicate whether "strict" bracketing is required. > Alter the contract of UnivariateRealSolverUtils.bracket() to handle piecewise constant functions > ------------------------------------------------------------------------------------------------ > > Key: MATH-700 > URL: https://issues.apache.org/jira/browse/MATH-700 > Project: Commons Math > Issue Type: Improvement > Affects Versions: 3.0 > Reporter: Sébastien Brisard > Priority: Minor > > The current contract of {{o.a.c.m.analysis.solvers.UnivariateRealSolverUtils.bracket(UnivariateRealFunction function, double initial, double lowerBound, double upperBound, int maximumIterations)}} states that > {quote} > This method attempts to find two values a and b satisfying > * {{lowerBound <= a < initial < b <= upperBound}} > * {{f(a) * f(b) <= 0}} > If f is continuous on [a,b], this means that a and b bracket a root of f. > {quote} > I don't think there is any problem with the current implementation. However, if f is constant, equal to zero on a whole interval, this implementation does not guarantee that the whole interval is bracketed. I therefore propose that the contract is changed to > * {{f(a) * f(b) < 0}} > This entails only a minor correction to the {{bracket()}} method: line 267 of UnivariateRealSolverUtils currently reads > ...{{while ((fa * fb > 0.0) && (numIterations < maximumIterations)}}... > I think it would be safe to replace this line with > ...{{while ((fa * fb >= 0.0) && (numIterations < maximumIterations)}}... > Do you agree in principle? I'll run the current tests to check that this change is indeed safe. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira