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https://issues.apache.org/jira/browse/MATH-562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13024947#comment-13024947
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Phil Steitz commented on MATH-562:
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Sorry for the slow response and lack of understanding. I still don't quite get
the "offset." What exactly does this mean? Isn't every point a potential
period start point? Maybe this is a root?
What I meant by "fitness" was some kind of reasonability test to ensure that
the data conform to the assumption of periodicity. Not necessary, but I can
imagine scenarios where piecing together a periodic interpolator from a set of
sample points would result in strange and/or not well-defined behavior. I
could be misunderstanding the setup, but isn't there a risk that values for
points near "cut points" are not well-defined? What I mean by a "cut point" is
a point near the end of the sample, say between the period sample point and the
"extra" point added after the end. There will be an interpolated value for
that point based on the "base" interpolator. The periodic interpolator will
return a value for that point based on translation / extrapolation (assuming I
am understanding the setup). If the underlying function really is periodic, we
have the right period and the base interpolator works perfectly, then these
values will be the same. If not, they could be different. How badly different
they can be is what I was referring to as "fitness."
In any case, I think this could be a useful addition and as long as we document
exactly what it does, I am +1 to add.
> "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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