Example 1

import java.text.*;
import com.imsl.math.*;

public class Spline2DInterpolateEx1 {
    
    private static double F(double x, double y) {
        return (x*x*x+y*y);
    }
    
    public static void main(String args[]) {
        int nData = 11;
        int outData = 2;
        double[][] fdata = new double[nData][nData];
        double[] xData = new double[nData];
        double[] yData = new double[nData];
        double x, y, z;
        
        // Set up grid
        for (int i = 0; i < nData; i++) {
            xData[i] = yData[i] = (double)i / ((double)(nData-1));
        }
        
        for (int i = 0; i < nData; i++) {
            for (int j = 0; j < nData; j++) {
                fdata[i][j] = F(xData[i], yData[j]);
            }
        }
        
        // Compute tensor-product interpolant
        Spline2DInterpolate spline =
                new Spline2DInterpolate(xData, yData, fdata);
        
        NumberFormat nf = NumberFormat.getInstance();
        nf.setMaximumFractionDigits(4);
        nf.setMinimumFractionDigits(4);
        
        // Print results
        System.out.println("   x        y     F(x, y)   " +
                "Interpolant   Error");
        for (int i = 0; i < outData; i++) {
            x = (double) i / (double) (outData);
            for (int j = 0; j < outData; j++) {
                y = (double) j / (double) (outData);
                z = spline.value(x, y);
                System.out.println(nf.format(x) + "   " + nf.format(y) + "   "
                        + nf.format(F(x,y)) + "       " + nf.format(z) +
                        "     " + nf.format(Math.abs(F(x,y)-z)));
            }
        }
    }
}

Output

   x        y     F(x, y)   Interpolant   Error
0.0000   0.0000   0.0000       0.0000     0.0000
0.0000   0.5000   0.2500       0.2500     0.0000
0.5000   0.0000   0.1250       0.1250     0.0000
0.5000   0.5000   0.3750       0.3750     0.0000