Numeric Integration with Trapezoidal Method

IntegralNumerica_src_numerical_integration_Main.java

package numerical.integration;

import java.io.InputStreamReader;
import java.util.ArrayList;

public class Main {

    static double[][] function_data;
    static double offset;
    static final boolean IS_IN_DEBUG_MODE = false;

    public static void main(String[] args) {
        // write your code here
        //integración numérica.

        InputStreamReader input = new InputStreamReader(System.in);
        /*formula trapecio = (b+B)/2 * h
                b
             h________
            /|        \
        *  /_|_________\
                    B
        */
        //contains coefficients for each variable and exponent.
        function_data = new double[][]{
                new double[]{1, 2}
        };
        offset = 1;
        double start_position = 0, end_position = 10;

        //aka = h
        double trapezoidHeight = 0.001;
        double number_rectangles = (end_position - start_position) / trapezoidHeight;
        double sum_of_area = 0;

        int counter = 0;
        for (double i = 0; i <= (end_position - trapezoidHeight); i += trapezoidHeight) {
            double area, minor_base, major_base;
            counter++;
            minor_base = computeFunction(i + start_position);
            major_base = computeFunction(i + start_position + trapezoidHeight);
            area = (minor_base + major_base) / 2 * trapezoidHeight;
            sum_of_area += area;
        }
        System.out.println("Area is: " + sum_of_area);
        System.out.println("Count is: " + counter);
        System.out.println("number_rects is: " + number_rectangles);


        /*
            int[][] foo = new int[][] {
                new int[] { 1, 2, 3 },
                new int[] { 1, 2, 3, 4},
            };

            System.out.println(foo.length); //2
            System.out.println(foo[0].length); //3
            System.out.println(foo[1].length); //4
         */

    }

    public static Double computeFunction(double x, double[][] data, double offset) {
        if (data[0].length < 2) {
            System.out.println("invalid data from computeFunction");
            return null;
        }
        double sum = 0;
        for (int i = 0; i < data.length; i++) {
            double power = Math.pow(x, data[i][1]);
            sum += power * data[i][0];

        }
        return sum + offset;
    }

    public static Double computeFunction(double x) {
        if (IS_IN_DEBUG_MODE) {
            String function = "f(x) =";
            System.out.println("Row           Values");
            for (int i = 0; i < function_data.length; i++) {
                function += " " + function_data[i][0] + "x^" + function_data[i][1] + " +";
            }
            function += " " + offset;
            System.out.println("Function f(x): \n" + function);
        }
        if (function_data[0].length < 2) {
            System.out.println("invalid data from computeFunction");
            return null;
        }
        double sum = 0;
        for (int i = 0; i < function_data.length; i++) {
            double power = Math.pow(x, function_data[i][1]);
            sum += power * function_data[i][0];

        }
        return sum + offset;
    }

}