package sansmodels;

public class HollowCylinder extends SANSModel{
 
    private double scale, coreRadius, shellRadius, background;
    private double deltaRho, length;

    //Default constructor
    public HollowCylinder() {
        scale = 1.0;
        coreRadius = 20.0;
        shellRadius = 30.0;
        length = 400.0;
        deltaRho = 3.e-6;
        background = 0.00;
        setNumberOfParameters(6);
        String[] parameters = {"Scale", "Core Radius (A)",
            "Shell Radius (A)", "Length (A)", "Contrast (A-2)",
            "Background (cm-1)"};
        setParametersText(parameters);
    }

    public HollowCylinder(double inScale, 
                     double inCoreRadius,
                     double inShellRadius,
                     double inLength,
                     double inDeltaRho,
                     double inBackground) {
        scale = inScale; 
        coreRadius = inCoreRadius;
        shellRadius = inShellRadius;
        length = inLength;
        deltaRho = inDeltaRho;
        background = inBackground;
        setNumberOfParameters(6);
        String[] parameters = {"Scale", "Core Radius (A)",
            "Shell Radius (A)", "Length (A)", "Contrast (A-2)",
            "Background (cm-1)"};
        setParametersText(parameters);
    }

    private double hollowCylinderFunc(double inQ, double inZ) {
        double gamma, bessarg1, bessarg2, lam1, lam2, t2, psi, sinarg;
        
        gamma = coreRadius/shellRadius;
        bessarg1 = inQ * shellRadius * Math.sqrt(1-(inZ*inZ));
        bessarg2 = inQ * coreRadius * Math.sqrt(1-(inZ*inZ));
        lam1 = 2.0*SpecialFunction.j1(bessarg1)/bessarg1;
        lam2 = 2.0*SpecialFunction.j1(bessarg2)/bessarg2;
        psi = 1.0/(1-(gamma*gamma))*(lam1 - gamma*gamma*lam2);
        
        sinarg = inQ*length*inZ/2.0;
        t2 = Math.sin(sinarg)/sinarg;
        
        return psi*psi*t2*t2;
    }
 
    public double getFormFactor(double inX) {

        int nord = 76;
        double va, vb, summ, zi, answer, yyy;
        double vol;
        va = 0.0;
        vb = 1.0;

        summ = 0.0;
        
        for(int i=0;i<nord;i++) {
            zi = (Gaussian.z76[i]*(vb-va) + vb + va)/2.0;
            yyy = Gaussian.w76[i]*hollowCylinderFunc(inX,zi);
            summ += yyy;
        }
         
        answer = (vb-va)/2.0*summ;
        
        answer *= deltaRho*deltaRho;
 
        vol = Math.PI*coreRadius*coreRadius*length;                             
        return answer*vol*1.0e8*scale*getStructureFactor().calculate(inX)
            + background;
    }

    public void setParameters(double[] inParameters) {
        scale = inParameters[0];
        coreRadius = inParameters[1];
        shellRadius = inParameters[2];
        length = inParameters[3];
        deltaRho = inParameters[4];
        background = inParameters[5];
    }
 
    public double[] getParameters() {
        double[] outParameters = new double[6];
        outParameters[0] = scale;
        outParameters[1] = coreRadius;
        outParameters[2] = shellRadius;
        outParameters[3] = length;
        outParameters[4] = deltaRho;
        outParameters[5] = background;
        return outParameters;
    }
}