package sansmodels;

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

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

    public HardSphereStruct(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 denom, dnum, alpha, beta, gamm, a, asq, ath, afor;
        double rca, rsa, calp, cbeta, cgam, prefac, c;

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

        denom = Math.pow((1.0-phi),4.0);
        dnum = Math.pow((1.0 + 2.0*phi),2.0);
        alpha = dnum/denom;
        beta = -6.0*phi*Math.pow((1.0 + phi/2.0),2.0)/denom;
        gamm = 0.5*phi*dnum/denom;
        
        a = 2.*inX*radius;
        asq = a*a;
        ath = asq*a;
        afor = ath*a;
        rca = Math.cos(a);
        rsa = Math.sin(a);
        calp = alpha*(rsa/asq - rca/a);
        cbeta = beta*(2.0*rsa/asq - (asq - 2.0)*rca/ath - 2.0/ath);
        cgam = gamm*(-rca/a +(4./a)*((3.*asq - 6.)*rca/afor +
               (asq - 6.)*rsa/ath +6./afor));
        prefac = -24.0*phi/a;
        c = prefac*(calp + cbeta + cgam);
        return  1.0/(1.0 - c);
    }

    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;
    }
}