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From "Yannick TANGUY (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-811) Improve event detection by selecting g function slope
Date Thu, 27 Sep 2012 13:48:08 GMT

    [ https://issues.apache.org/jira/browse/MATH-811?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13464732#comment-13464732
] 

Yannick TANGUY commented on MATH-811:
-------------------------------------

Hello Luc,

Ok, but could you explain a little bit please ? 

As I understand the code, this value is true when g0 > 0, and is updated in stepAccepted
method. There's no getter for this value, and it's only used once in the test "if (g0Positive
^ (gb >= 0))", so I guess it could be replaced by a test on ga.
One thing I don't understand (and it may be the point you notice in the comment "Simulated
sign of g0 (we cheat when crossing events)." is the following code in stepAccepted : 
{noformat}
        if (pendingEvent && (FastMath.abs(pendingEventTime - t) <= convergence))
{
            // force the sign to its value "just after the event"
            previousEventTime = t;
            g0Positive        = increasing;
            nextAction        = handler.eventOccurred(t, y, !(increasing ^ forward));
        } else {
            g0Positive = g0 >= 0;
            nextAction = EventHandler.Action.CONTINUE;
        }
{noformat}
-> the value "increasing" relates to g function, and not to g0 value. 

If removing g0positive field is a problem, we could put it again, but I don't understand the
reasons yet.
                
> Improve event detection by selecting g function slope
> -----------------------------------------------------
>
>                 Key: MATH-811
>                 URL: https://issues.apache.org/jira/browse/MATH-811
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.1
>            Reporter: Yannick TANGUY
>         Attachments: JIRA-811_slope_selection.patch, JIRA-811_slope_selection_V2.patch,
JIRA-811_slope_selection_with_spaces.patch
>
>
> We would like to select g function slope in CommonsMath event detection feature.
> This would improve event detection for the final user (the possibility to ignore some
events, and less computation time) and also correct a bug found while using OREKIT (see https://www.orekit.org/forge/issues/104)
in our applications. 
> The modification consists in adding a method (getSlopeSelection() : int) in EventHandler,
and modifying one conditionnal in the method evaluateStep (class EventState). 
> We can provide modified code and unitary tests for this feature.

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