[jira] [Closed] (MATH-1471) BicubicInterpolatingFunction not interpolating correctly for non discrete y value

["Tom (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-1471?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tom closed MATH-1471.
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    Resolution: Invalid

> BicubicInterpolatingFunction not interpolating correctly for non discrete y value
> ---------------------------------------------------------------------------------
>
>                 Key: MATH-1471
>                 URL: https://issues.apache.org/jira/browse/MATH-1471
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.6.1
>         Environment: JDK 1.8.0_181 
>            Reporter: Tom
>            Priority: Major
>         Attachments: ApacheCommonsMathBiInterpolationTests.zip, Interpolate.java, InterpolateTest.java
>
>
> Upon performing a bicubic interpolation with two point (x0, y0) and (x1, y1), the returned bicubic interpolating function returned returns the same result for variations in the estimated y value. 
> For example, my inputs are (20, 20) and (25, 25) with f(20, 20) = 64 and f(25, 25) = 6468.
> When I get the bicubic interpolating function for this and vary the estimated x, it works fine. For (21, 20), the function returns 730.016. When I input (20, 21), the function returns 64, which is f(20, 20). For any y value in between 20 and 25, the result is 64. This is the case for any function for which the y estimate is different from the value on the points. 
> In other instances, it is varying x values that result in the same result while varying y estimates seem to work as expected.



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