/**copyright by Emanuele Dalla Torre - Technion 2002*/

class KPBand
	{
	double minZ, maxZ;
	boolean conduction;

	KPBand(double minZ, double maxZ, boolean conduction)
		{this.minZ=minZ; this.maxZ=maxZ; this.conduction=conduction;}

	double derivate(KronigPenney kp)
		{
		//System.out.print(start+" "+step+"\n");
		final int N=20;
		final long pointsNumber=(long)10000;
		double[] k=new double[N], z=new double[N];
		double start=conduction?minZ:maxZ, end=conduction?maxZ:minZ;
		double step=(end-start)/pointsNumber;

		//take data
		int n=N;//needed for NaN!
		for(int j=0;j<N;j++)
			{
			z[j+n-N]=start+(j)*step;
			k[j+n-N]=kp.k(z[j+n-N]);
			if (Double.isNaN(k[j+n-N])){n--;}
			}
		//derivate once
		for(int j=0;j<n-1;j++)
			{z[j]=(z[j+1]-z[j])/(k[j+1]-k[j]);}
		//derivate twice
		for(int j=0;j<n-2;j++)
			{z[j]=(z[j+1]-z[j])/(k[j+1]-k[j]);}
		//average
		double d2=0;
		for(int j=0;j<n-2;j++)
			{d2=d2+z[j];}
		System.out.print("step="+step+"derivate2="+d2/(n-2)+"conduction= "+conduction+" n="+n+"\n");
		System.out.print("start="+start+"\n");
		System.out.print("end="+end+"\n");
		return(d2/(n-2));
		}
	}