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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-562) "UnivariateRealPeriodicInterpolator"
Date Fri, 22 Apr 2011 19:05:05 GMT

    [ https://issues.apache.org/jira/browse/MATH-562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13023337#comment-13023337
] 

Phil Steitz commented on MATH-562:
----------------------------------

Indeed, why not?  I am not following exactly what is being proposed, though.  Is the idea
that the data are assumed to be coming from a periodic function with known period?  Is there
any constraint on the number of periods that the sample data is supposed to represent, or
are we assuming that it represents just one period with some points extending before and after?
 I guess the application is to extend the domain of the interpolating function outside of
the domain determined by the data?  Don't you maybe need two parameters for "extend" (number
before beginning of function period and number after) and maybe even two "offset" parameters
(distance between beginning of the period and the first "interior" domain value and between
last "interior" domain value and end of the period)?  Could well be I am misunderstanding
the setup here.  Another thing that I don't quite get is it would seem some kind of fitness
measure would be needed to ensure that the designation of the "interior" points is consistent
with periodicity (i.e., behavior in a neighborhood of period start and end points is similar).

> "UnivariateRealPeriodicInterpolator"
> ------------------------------------
>
>                 Key: MATH-562
>                 URL: https://issues.apache.org/jira/browse/MATH-562
>             Project: Commons Math
>          Issue Type: New Feature
>            Reporter: Gilles
>            Assignee: Gilles
>            Priority: Minor
>             Fix For: 3.0
>
>
> It would be an interpolator implementation that assumes that the data to be interpolated
is periodic. Thus values that are outside of the range can be passed to the interpolation
function:
> They will be wrapped into the initial range before being passed to the class that actually
computes the interpolation.
> The constructor prototype would be:
> {code}
> /**
>  * Builds an interpolator.
>  *
>  * @param interpolator Interpolator.
>  * @param period Period.
>  * @param offset Offset.
>  * @param extend Number of points to be appended at the beginning and
>  * end of the sample arrays in order to avoid interpolation failure at
>  * the (periodic) boundaries of the orginal interval. The value is the
>  * number of sample points which the original {@code interpolator} needs
>  * on each side of the interpolation point.
>  */
> public UnivariateRealPeriodicInterpolator(UnivariateRealInterpolator interpolator,
>                                           double period,
>                                           double offset,
>                                           int extend) {
>     // ...
> }
> {code}
> Would it be useful to have that in CM?

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