Class Integration

MathParser/src/com/aghajari/math/custom/Integration.java:8–410

// https://github.com/gbenroscience/ParserNG/blob/master/src/main/java/math/numericalmethods/Integration.java
public class Integration {

    private FunctionWrapper function = null;    // Function to be integrated
    private boolean setFunction = false;        // = true when Function set
    private double lowerLimit = Double.NaN;     // Lower integration limit
    private double upperLimit = Double.NaN;     // Upper integration limit
    private boolean setLimits = false;          // = true when limits set

    private int glPoints = 0;                   // Number of points in the Gauss-Legendre integration
    private boolean setGLpoints = false;        // = true when glPoints set
    private int nIntervals = 0;                 // Number of intervals in the rectangular rule integrations
    private boolean setIntervals = false;       // = true when nIntervals set

    private double integralSum = 0.0D;          // Sum returned by the numerical integration method
    private boolean setIntegration = false;     // = true when integration performed

    // ArrayLists to hold Gauss-Legendre Coefficients saving repeated calculation
    private static ArrayList<Integer> gaussQuadIndex = new ArrayList<Integer>();         // Gauss-Legendre indices
    private static ArrayList<double[]> gaussQuadDistArrayList = new ArrayList<double[]>();  // Gauss-Legendre distances
    private static ArrayList<double[]> gaussQuadWeightArrayList = new ArrayList<double[]>();// Gauss-Legendre weights

    // Iterative trapezium rule
    private double requiredAccuracy = 0.0D;     // required accuracy at which iterative trapezium is terminated
    private double trapeziumAccuracy = 0.0D;    // actual accuracy at which iterative trapezium is terminated as instance variable
    private static double trapAccuracy = 0.0D;  // actual accuracy at which iterative trapezium is terminated as class variable
    private int maxIntervals = 0;               // maximum number of intervals allowed in iterative trapezium
    private int trapeziumIntervals = 1;         // number of intervals in trapezium at which accuracy was satisfied as instance variable
    private static int trapIntervals = 1;       // number of intervals in trapezium at which accuracy was satisfied as class variable

    // CONSTRUCTORS

    // Constructor taking function to be integrated
    public Integration(FunctionWrapper intFunc) {
        this.function = intFunc;
        this.setFunction = true;
    }

    // Constructor taking function to be integrated and the limits
    public Integration(FunctionWrapper intFunc, double lowerLimit, double upperLimit) {
        this.function = intFunc;
        this.setFunction = true;
        this.lowerLimit = lowerLimit;
        this.upperLimit = upperLimit;
        this.setLimits = true;
    }

    // SET METHODS

    // Set function to be integrated
    public void setFunction(FunctionWrapper intFunc) {
        this.function = intFunc;
        this.setFunction = true;
    }

    // Set limits
    public void setLimits(double lowerLimit, double upperLimit) {
        this.lowerLimit = lowerLimit;
        this.upperLimit = upperLimit;