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

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

Thomas Swinicki created MATH-1471:
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             Summary: 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: Thomas Swinicki


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. 



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