[
https://issues.apache.org/jira/browse/MATH-1138?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14175947#comment-14175947
]
Thomas Neidhart commented on MATH-1138:
---------------------------------------
I understand and appreciate the effort that has been put into this issue, but I
just wanted to point out that we might create a potential regression here for
people that have been using the interpolator with less than 3 data points.
To be honest, I do not know exactly how to proceed, as the current code clearly
improves the results, maybe we should explicitely note this change in the
release notes.
> BicubicSplineInterpolator is returning incorrect interpolated values
> --------------------------------------------------------------------
>
> Key: MATH-1138
> URL: https://issues.apache.org/jira/browse/MATH-1138
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 3.3
> Reporter: Adam Bedrossian
> Fix For: 3.4
>
> Attachments: Interpolated Values from CM and MatLab.docx
>
>
> I have encountered a use case with the BicubicSplineInterpolator where the
> interpolated values that are being returned seem incorrect. Furthermore, the
> values do not match those generated by MatLab using the interp2 'cubic'
> method.
> Here is a snippet of code that uses the interpolator:
> double[] xValues = new double[] {36, 36.001, 36.002};
> double[] yValues = new double[] {-108.00, -107.999, -107.998};
> double[][] fValues = new double[][] {{1915, 1906, 1931},
> {1877, 1889, 1894},
> {1878, 1873, 1888}};
> BicubicSplineInterpolator interpolator = new
> BicubicSplineInterpolator();
> BicubicSplineInterpolatingFunction interpolatorFunction =
> interpolator.interpolate(xValues, yValues, fValues);
> double[][] results = new double[9][9];
> double x = 36;
> int arrayIndexX = 0, arrayIndexY = 0;
> while(x <= 36.002) {
> double y = -108;
> arrayIndexY = 0;
> while (y <= -107.998) {
> results[arrayIndexX][arrayIndexY] =
> interpolatorFunction.value(x, y);
> System.out.println(results[arrayIndexX][arrayIndexY]);
> y = y + 0.00025;
> arrayIndexY++;
> }
> x = x + 0.00025;
> arrayIndexX++;
> }
> Attached is a grid showing x and y values and the corresponding interpolated
> value from both commons math and MatLab.
> The values produced by commons math are far off from those created by MatLab.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
