package sansmodels;

public class BE_RPA extends SANSModel{
 
    private double k, Lb, h, b, Cs, alpha, C, background;

    //Default constructor
    public BE_RPA() {
        k = 10.0;
        Lb = 7.1;
        h = 12.0;
        b = 10.0;
        Cs = 0.0;
        alpha = 0.05;
        C = 0.7;
        background = 0.0;
        setNumberOfParameters(8);
        String[] parameters = {"K (barns)","Lb (A)","h (A-3)","b (A)",
            "Cs (mol/L)","alpha","C (mol/L)","Background (cm-1)"};
        setParametersText(parameters);
    }

    public BE_RPA(double ink, double inLb, 
                  double inh, double inb, 
                  double inCs, double inalpha, 
                  double inC, double inBackground) {
        k  = ink;
        Lb = inLb;
        h  = inh;
        b  = inb;
        Cs = inCs;
        alpha = inalpha;
        C  = inC;
        background = inBackground;
        setNumberOfParameters(8);
        String[] parameters = {"K (barns)","Lb (A)","h (A-3)","b (A)",
            "Cs (mol/L)","alpha","C (mol/L)","Background (cm-1)"};
        setParametersText(parameters);
    }

    public double getFormFactor(double inX) {
        double Ca, Csa, k2, r02, q2, Sq;
       
        Ca = C*6.022136e-4;
        Csa = Cs*6.022136e-4;
        k2 = 4.0*Math.PI*Lb*(2.0*Cs + alpha*Ca);

        r02 = 1./alpha/Math.sqrt(Ca)*(b/Math.sqrt(48.0*Math.PI*Lb));
        q2 = inX*inX;
        
        Sq = k*1.0/(4.0*Math.PI*Lb*alpha*alpha)*(q2 + k2) 
             / (1.0+ r02*r02*(q2+k2)*(q2-(12.0*h*Ca/b/b)));
        return Sq*getStructureFactor().calculate(inX) + background;
    }

    public void setParameters(double[] inParameters) {
        k = inParameters[0];
        Lb = inParameters[1];
        h = inParameters[2];
        b = inParameters[3];
        Cs = inParameters[4];
        alpha = inParameters[5];
        C = inParameters[6];
        background = inParameters[7];
    }
 
    public double[] getParameters() {
        double[] outParameters = new double[8];
        outParameters[0] = k;
        outParameters[1] = Lb;
        outParameters[2] = h;
        outParameters[3] = b;
        outParameters[4] = Cs;
        outParameters[5] = alpha;
        outParameters[6] = C;
        outParameters[7] = background;
        return outParameters;
    }
}