regression.java~1~

来自「一个一元曲线多项式数值演示例子」· JAVA~1~ 代码 · 共 69 行

package numbercruncher.program10_2;

import numbercruncher.mathutils.DataPoint;
import numbercruncher.mathutils.RegressionPolynomial;
import numbercruncher.matrix.ColumnVector;
import numbercruncher.matrix.MatrixException;

/**
 * PROGRAM 10-2: Polynomial Regression
 *
 * Demonstrate polynomial regression by fitting a polynomial
 * to a set of data points.
 */
public class Regression
{
    private static final int   MAX_POINTS = 20;
    private static final float TWO_PI     = (float) (2*Math.PI);
    private static final float H          = TWO_PI/MAX_POINTS;

    /**
     * Main program.
     * @param args the array of runtime arguments
     */
    public static void main(String args[])
    {
        int   degree = 3;
        float testX  = (float) Math.PI;

        try {
            RegressionPolynomial poly =
                    new RegressionPolynomial(degree, MAX_POINTS);

            // Compute MAX_POINTS data points along the sine curve
            // between 0 and 2*pi.
            for (int i = 0; i < MAX_POINTS; ++i) {
                float x = i*H;
                float y = (float) Math.sin(x);
                poly.addDataPoint(new DataPoint(x, y));
            }

            // Compute and print the regression polynomial.
            System.out.print("y = ");
            ColumnVector a = poly.getRegressionCoefficients();
            System.out.print(a.at(0) + " + " + a.at(1) + "x");
            for (int i = 2; i <= degree; ++i) {
                System.out.print(" + " + a.at(i) + "x^" + i);
            }
            System.out.println();

            // Compute an estimate.
            System.out.println("y(" + testX + ") = " +
                               poly.at(testX));

            // Print the warning if there is one.
            String warning = poly.getWarningMessage();
            if (warning != null) {
                System.out.println("WARNING: " + warning);
            }
        }
        catch(Exception ex) {
            System.out.println("\nERROR: " + ex.getMessage());
        }
    }
}
/*
Output:
y = -0.14296114 + 1.8568094x + -0.87079257x^2 + 0.09318722x^3
y(3.1415927) = -0.014611721
*/