package sansmodels;

public class HardDiskStruct extends StructureFactor{
 
    private double radius, volumeFraction;

    //Default constructor
    public HardDiskStruct() {
        radius = 50.0;
        volumeFraction = 0.2;
        setNumberOfParameters(2);
        String[] parameters = {"Radius (A)", "Vol Fraction (0-1)" };
        setParametersText(parameters);
    }

    public HardDiskStruct(double inRadius, double inVolFrac) {
        radius = inRadius;
        volumeFraction = inVolFrac;
        setNumberOfParameters(2);
        String[] parameters = {"Radius (A)", "Vol Fraction (0-1)" };
        setParametersText(parameters);
    }

    public double calculate(double inX) {
        double chi, a, b, g, qr, qr2;
        double ta, tb, tg, vstruc, bess1qr, bess0qr, bess1qr2;

        double phi = volumeFraction;
        if (phi > 0.99999) phi = 0.99999;

        g = 1.0/(Math.pow((1.0-phi),1.5));
        chi = (1.0+phi)/((1.0-phi)*(1.0-phi)*(1.0-phi));
        a = (1.0+(2.0*phi - 1.0)*chi + 2.0*phi*g)/phi;
        b = ((1-phi)*chi - 1.0 - 3.0*phi*g)/phi;
        qr = inX*radius;
        qr2 = 2.0*qr;
        bess0qr = SpecialFunction.j0(qr);
        bess1qr = SpecialFunction.j1(qr);
        bess1qr2 = SpecialFunction.j1(qr2);
       
        ta = a*bess1qr*bess1qr/qr/qr;
        tb = b*bess0qr*bess1qr/qr;
        tg = g*bess1qr2/qr;
        vstruc = 1.0 + 4.0*phi*(ta+tb+tg);
        return 1.0/vstruc;
    }

    public void setParameters(double[] inParameters) {
        radius = inParameters[0];
        volumeFraction = inParameters[1];
    }
 
    public double[] getParameters() {
        double[] outParameters = new double[2];
        outParameters[0] = radius;
        outParameters[1] = volumeFraction;
        return outParameters;
    }
}