package com.imsl.test.example.stat.distributions;

import com.imsl.math.*;
import com.imsl.stat.distributions.*;
import java.text.DecimalFormat;
/**
 * <p>
 * Evaluates the gamma probability distribution.</p>
 * <p>
 * This example evaluates the gamma density, gradient, and hessian for a small
 * sample of data.</p>
 *
 * @see <a href="GammaPDEx1.java">Code</a>
 * @see <a href="doc-files/GammaPDEx1.out">Output</a>
 */

public class GammaPDEx1 {

    public static void main(String[] args) throws Exception {

        double x[] = {
            1.015998e0, 0.2677489e0, 2.198958e0, 1.784697e0, 0.691063e0,
            0.992409e0, 0.5466309e0, 1.154601e0, 2.613015e0, 1.219826e0
        };

        double[] values = new double[x.length];
        double a = 3.0;
        double b = 2.0;

        GammaPD gamma = new GammaPD();

        for (int i = 0; i < x.length; i++) {
            values[i] = gamma.pdf(x[i], a, b);
        }

        PrintMatrixFormat pmf = new PrintMatrixFormat();
        pmf.setNumberFormat(new DecimalFormat("0.00000000"));

        PrintMatrix pm = new PrintMatrix("Gamma(3.0,2.0) pdf values at x=");
        pm.print(pmf, x);

        pm.setTitle("f(x;3,2)=");
        pm.print(pmf, values);

        double[] gradient = gamma.getPDFGradientApproximation(x[0], a, b);

        String title=String.format("Gradient of f(x;3,2) at x= %1.8f",x[0]);
        pm.setTitle(title);
        pm.print(pmf, gradient);

        double[][] hessian = gamma.getPDFHessianApproximation(x[0], a, b);

        title=String.format("Hessian of f(x;3,2) at x= %1.8f",x[0]);
        pm.setTitle(title);
        pm.print(pmf, hessian);
    }
}