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From "Adam Bedrossian (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MATH-1138) BicubicSplineInterpolator is returning incorrect interpolated values
Date Fri, 11 Jul 2014 18:54:04 GMT

     [ https://issues.apache.org/jira/browse/MATH-1138?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Adam Bedrossian updated MATH-1138:
----------------------------------

    Description: 
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.

  was:
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.


> 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
>         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.



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