[jira] [Commented] (MATH-1635) AkimaSplineInterpolator overshoots graph

["Gilles Sadowski (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MATH-1635?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17451462#comment-17451462 ] 

Gilles Sadowski commented on MATH-1635:
---------------------------------------

I've added a unit test in commit c6094cf9e0f99f71e92e678fef08202fe3301069 (set to "@Ignore").
It would be useful to know whether another implementation exhibits the same behaviour.

> AkimaSplineInterpolator overshoots graph
> ----------------------------------------
>
>                 Key: MATH-1635
>                 URL: https://issues.apache.org/jira/browse/MATH-1635
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.6.1
>            Reporter: Gili
>            Priority: Major
>
> AkimaSplineInterpolator is not supposed to overshoot points on the graph, but the following testcase seems to show it doing exactly that:
>  
> {code:java}
> double[] x = {1616326459, 1616326545, 1616326555, 1616326588, 1616326663, 1616326760,
>  1616326770, 1616326792, 1616326856, 1616326964, 1616327028, 1616327233, 1616327426,
>  1616327469, 1616327619, 1616327910, 1616328038, 1616328178, 1616328414, 1616328747,
>  1616328983, 1616329316, 1616329864, 1616329875};
> double[] y = {2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0, 2.0,
>  2.0, 2.0, 2.0, 2.0, 2.0, 3.0};
> AkimaSplineInterpolator interpolator = new AkimaSplineInterpolator();
> PolynomialSplineFunction interpolate = interpolator.interpolate(x, y);
> double value = interpolate.value(1616329584);
> System.out.println("Interpolated value is: " + value + ". Expected: 2.0"); {code}
>  
> When I run the testcase I get 
> {code:java}
> Interpolated value is: -3.9681889999323374. Expected: 2.0 {code}
>  
> I am also quite confused about where to find the latest version of this library. I know that 3.6.1 is very out of date but I am reluctant to depend on SNAPSHOT dependencies, especially if they sit outside of Maven Central. What do you recommend?
>  



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